How to Compare Roofing Slate Quotations

I've been comparing roofing slate quotations for over twenty years. The first thing I tell anyone who walks into my office with three quotes from three suppliers is this: put them side by side, and don't look at the bottom line yet.

Because the bottom line lies.

One supplier quotes $11.50 per m². Another quotes $14.00. A third quotes $9.80. Most buyers circle the $9.80 and move on. Nine times out of ten, that's the quote that ends up costing the most by the time the container arrives at their warehouse. Not because the supplier was dishonest — though that happens too — but because the quote was written in a way that made certain costs invisible until it was too late to renegotiate.

Comparing quotations is not about finding the lowest number. It's about making three documents speak the same language, then reading what each one says — and what each one doesn't say. Here's how I do it, step by step.

Step 1: Make All Quotes Speak the Same Language

Before you can compare anything, you need every quotation on the same footing. That means four normalisations:

Same Incoterm. If one supplier quotes FOB Shanghai and another quotes CIF Rotterdam, you cannot compare them directly. FOB means the supplier's responsibility ends when the goods cross the ship's rail at the port of loading. CIF means the supplier pays for freight and insurance all the way to your destination port. A CIF quote will always look higher than an FOB quote for the same slate — but that doesn't mean the CIF supplier is more expensive. It means they're including costs the FOB supplier is leaving for you to arrange.

To compare fairly, convert all quotes to the same base. I prefer to normalise everything to FOB port of loading and then add ocean freight and insurance separately, because that way I can see the true material cost. If a supplier gives you CIF, ask them to break out the ocean freight and insurance. If they refuse, that's a signal — the freight quote might include a margin.

Same currency. Obvious, but I've seen quotes in USD, EUR and RMB sitting on the same desk. Convert everything to one currency using the rate on the day of the quote, and note the rate. If the euro moves 3% before you place the order, your "cheapest" quote might not be cheapest anymore.

Same unit. Some suppliers quote per piece. Others quote per square metre. A few quote per tonne. Per-piece quotes are the most dangerous because a "piece" can be any size — a 400×200 slate and a 500×250 slate are both one piece, but one covers 40% more roof area. Convert everything to price per square metre before you compare. If the supplier quotes per piece, ask for the coverage per piece (accounting for headlap) and divide.

Same quantity. A quote for 500 m² and a quote for 5,000 m² are not comparable. Volume discounts in slate are real — a 20ft container order (typically 900–1,100 m²) will get a better per-m² price than a half-container trial order. When asking for quotes, give all suppliers the same target quantity.

Step 2: The Unit Price Illusion

Once all quotes are normalised, look at the unit price. But don't stop there — ask what's behind that number.

A roofing slate at $12.00 per m² sounds straightforward. But what thickness is that? What grade? What colour selection? What tolerance?

Thickness is the biggest hidden multiplier. The same slate from the same quarry at 5–7 mm thick might cost $11.00 per m². At 7–9 mm, the same slate jumps to $13.50 — a 20% difference. Both are "roofing slate." Both pass the same EN 12326 or ASTM C406 tests. But one has more material in it, weighs more per square metre, and lasts longer in severe weather. If one supplier quotes 5–7 mm and another quotes 7–9 mm, the price gap isn't a discount — it's a different product. Read our full guide to slate thickness to understand which range your project actually needs.

Grade is the second multiplier. A supplier might offer "Grade A" at one price and "Grade B" at a lower price, but grade definitions vary. Under EN 12326 and ASTM C406, slate is graded by water absorption, flexural strength, freeze-thaw resistance and weathering behaviour. A supplier's internal "Grade A" might mean "hand-selected for colour uniformity" — a cosmetic standard, not a performance standard. When a quote looks too cheap, ask: what testing standard defines this grade, and can you share the test report with a batch number? If the report doesn't carry a batch number linking it to your production run, it's a brochure, not a certificate. We cover this in detail in our guide to reading roofing slate test reports.

Colour selection also affects price. A "mixed grey" pulled straight off the line is cheaper than a sorted, uniform grey selected for a heritage project. If one supplier's price is 15% lower, check whether they're quoting random colour or selected colour. Both are legitimate products — but they're not the same product.

So when you see a unit price, the real question is: what specification produced that number? If a supplier can't answer that question in one sentence, the quote is incomplete.

Step 3: Packing — The Silent Cost

Packing is where I see the most cost surprises. And it's the line item most buyers skip entirely.

A quotation might say "packing included" and leave it at that. But "packing" can mean a stack of slate on a wooden pallet with two steel straps — the bare minimum — or it can mean a close wooden crate with internal timber bracing, corner protectors, a moisture barrier, and a labelled batch card. The difference in cost between these two packing standards runs from $0.50 to $1.50 per m². On a 1,000 m² order, that's $500 to $1,500 — not huge, but enough to flip the ranking of two quotes that look identical on unit price.

More importantly, inadequate packing leads to breakage in transit. Ocean shipping involves weeks of vibration, humidity swings, and container handling. Slate packed loosely on a pallet with thin straps will shift. Corners chip. Edge pieces crack. A normal breakage rate for well-packed roofing slate is 1–3%. Poorly packed slate can see 5% or more — and that's 50 extra broken slates on a 1,000 m² order. At $14.00 per m², 50 m² of breakage is $700 in material you paid for but can't install.

When you compare quotes, ask each supplier to specify:

• Pallet or crate (and if pallet, what kind — two-way or four-way entry)
• Strapping material and number of bands
• Corner protectors: yes or no
• Moisture barrier (plastic wrap or desiccant): yes or no
• Labels and batch cards: yes or no
• Pieces per pallet and pallets per container

If a supplier won't commit to these details in writing, factor in a 3–5% breakage allowance when comparing their price. If they do commit, 1% is usually sufficient. That difference alone can move a "cheaper" quote to a more expensive one.

Step 4: Payment Terms as Effective Price

Two suppliers quote the same $13.00 per m². One asks for 30% deposit, 70% on copy of bill of lading. The other wants 50% deposit, 50% before loading. Or — and I've seen this from suppliers chasing volume — they offer 100% after delivery against documents.

These are not the same price.

Money has a time value. A 50% deposit ties up more of your cash earlier. If your company's cost of capital is 8% per year and the production cycle is 45 days, the difference between 30% upfront and 50% upfront on a $40,000 order is roughly $130 — small, but it adds up across multiple orders. More importantly, payment terms signal how much the supplier trusts their own product. A supplier who insists on 100% before shipment is telling you something. A supplier who accepts 70% on bill of lading is giving you leverage — if the goods arrive damaged or wrong, you still hold the final payment.

The standard in Chinese roofing slate export is 30% advance by T/T, 70% balance by T/T against a copy of the bill of lading. If a supplier deviates from this, ask why. A quote with an L/C (letter of credit) requirement adds roughly 2–3% in bank fees and processing costs — factor that into your comparison.

Step 5: What's NOT in the Quote

This is the step most buyers never take. And it's the one that saves the most money.

Take a red pen and circle everything your project needs that the quote doesn't mention. Every circled item is a cost you'll pay later — either to the supplier as a "supplement" or to a third party.

Here's a checklist of items I look for in every quote. If any of these are missing, I add an estimated cost:

• Inland freight to port of loading. A "FOB Jiujiang" quote is technically invalid — Jiujiang is an inland city. The nearest operational port is Jiujiang Port on the Yangtze, but most slate exports go through Shanghai or Ningbo. If a supplier says "FOB Shanghai" but their factory is in Jiujiang, the inland freight from factory to Shanghai (about 600 km by truck) should be included in their FOB price. If they haven't itemised it, ask. Inland trucking for a 20ft container on this route typically runs $400–$700. That's $0.40–$0.70 per m² on a 1,000 m² order — enough to change a ranking.
• Port handling charges (THC). Terminal handling charges at the port of loading can add $100–$200 per container. Some FOB quotes include this; many don't. Ask.
• Documentation fees. Commercial invoice, packing list, bill of lading, certificate of origin, phytosanitary certificate if required — some suppliers charge $50–$150 for the documentation pack. Others include it. When comparing, check.
• Container loading. Who loads the container — the factory or a third-party warehouse? If the supplier's FOB price doesn't include container stuffing, you'll pay a warehouse $100–$200 to do it.
• Quarry certificate or test report with batch number. If the supplier mentions a test report but doesn't include it with the shipment, you may need to pay for a separate test later — or, worse, discover the slate doesn't meet spec after it's already on your roof.

When I finish this exercise, I often find that the quote with the lowest headline price has four or five circled items, while the "expensive" quote has everything included. Add up the circled items as estimated costs, recalculate, and the ranking usually changes.

FOB vs CIF: Line-by-Line Comparison

Because the hub page specifically asks about FOB vs CIF, here's a side-by-side breakdown of what each Incoterm typically includes and excludes in a roofing slate shipment from China:

One important note: CIF includes only minimum marine insurance — typically Institute Cargo Clauses (C), which covers major losses (fire, sinking, collision) but not partial damage from handling or moisture. For roofing slate, where breakage and moisture damage are the main risks, consider upgrading to Clauses (A) or arranging your own policy. The premium difference is small — usually 0.1–0.3% of the cargo value — but the coverage difference is significant.

My recommendation for first-time importers: start with CIF for your first order so the supplier handles the freight, then switch to FOB with your own freight forwarder once you're comfortable with the process. This way you learn the product and supplier on the first order without also managing logistics for the first time.

The Red Flag Checklist

After twenty years and hundreds of quotations, here are the red flags that make me set a quote aside regardless of price:

• No port of loading specified. "FOB China" is not a port. If the supplier won't name the port, the inland freight is hidden. "FOB Shanghai" or "FOB Ningbo" — those are ports.
• No thickness range. "6mm" is a nominal thickness, not a range. Roofing slate is a natural product; it has a tolerance. "5–7 mm" or "7–9 mm" tells you the floor and ceiling. A single number tells you nothing.
• No grade definition. "Grade A" without a standard reference is marketing. "EN 12326 Grade T1, S1, A1" or "ASTM C406 Grade S1" is a specification.
• No packing spec. "Standard export packing" is not a specification. Pallet, crate, straps, corner protectors, moisture barrier — ask for each one.
• Quote valid for 30 days but material is "in stock." Natural slate doesn't sit in stock for long at a factory that's running. "In stock" often means "leftover from another order" — which may be a different colour batch.
• Price dramatically lower than market. If the going rate for 7–9 mm grey slate is $13–15 per m² FOB and someone quotes $8.50, something is off. It might be 4–5 mm slate sold as "roofing grade." It might be rejects that didn't pass sorting. It might be a different quarry entirely. A price 30% below market is not a bargain — it's a different product with a familiar label.

If you want a structured approach to vetting suppliers before you even ask for quotes, our ten questions for roofing slate suppliers covers the qualifying stage. And if you're new to the entire sourcing process — finding suppliers, verifying factories, requesting samples — the sourcing guide walks you through it step by step.

Putting It Together: A Worked Example

Let me show you how this works in practice. Here's a real comparison from a client who came to me last year with three quotes for a 1,000 m² order of grey roofing slate, 7–9 mm, 500×250 mm:

Supplier A: $12.50/m², FOB Shanghai, 30/70 payment, packing "included," no further detail. Test report available on request, no batch number mentioned.

Supplier B: $14.00/m², FOB Shanghai, 30/70 payment, wooden crate packing with corner protectors and moisture barrier (itemised at $0.80/m² within the unit price). Test report with batch number included with shipment.

Supplier C: $10.80/m², CIF Rotterdam, 50/50 payment, "standard export packing." No test report mentioned.

At first glance, Supplier C looks cheapest at $10.80. But let's normalise:

Supplier C is CIF Rotterdam. To convert to FOB equivalent, I subtract estimated ocean freight and insurance for a 20ft container from Shanghai to Rotterdam — roughly $1,800–$2,500 depending on the season. At $2,200 for 1,000 m², that's $2.20/m². So Supplier C's FOB equivalent is approximately $8.60/m². That's 30% below Supplier A and 40% below Supplier B. Red flag.

I asked the client to request a thickness specification from Supplier C. The answer came back: "4–6 mm." That's not 7–9 mm — it's a thinner, lighter product. At 4–6 mm, $8.60/m² FOB is a fair market price. But it's a different product. If the client needed 7–9 mm for a cold-climate roof with freeze-thaw exposure, Supplier C's slate would be under-specified regardless of price.

I also asked about the packing. "Standard export packing" turned out to be pallet-and-strap with no corner protectors. I estimated 4% breakage instead of the 1% I'd expect from Supplier B's crated packing. At 4% of 1,000 m² at $10.80/m², that's $432 in lost material.

And the 50/50 payment terms on a $10,800 order meant an extra $2,500 tied up for an additional 3–4 weeks compared to 30/70. At the client's cost of capital, that's another $40–$60 in effective cost.

After normalisation, here's how the quotes actually stacked up (all figures FOB Shanghai equivalent, per m²):

The client chose Supplier B. Not because B was the cheapest — B was the most expensive on the headline number. But B was the only supplier who quoted the correct thickness, specified the packing, attached a batch-numbered test report, and offered standard 30/70 terms. Supplier A was a reasonable second choice but couldn't provide a batch-numbered report. Supplier C was eliminated — not because they were dishonest, but because they were quoting a different product.

That's the point. Comparing quotations isn't about arithmetic. It's about making sure you're comparing the same thing — and then choosing the supplier who's given you enough information to trust the number.

Related Reading

• How to Source Roofing Slate from China — the full sourcing journey from finding suppliers to container loading, step by step
• Questions to Ask a Roofing Slate Supplier — ten questions that do the filtering for you before you ever ask for a quote
• Roofing Slate Cost: Price per m² & per Roof — what a natural slate roof really costs, including material, labour and import factors
• Roofing Slate Buying Guide & Checklist — the complete buying checklist for first-time slate importers
• Roofing Slate Inspection Checklist — what to check when the container arrives at your warehouse