The short answer: ask what system is going on, what is inside it, how it is fixed, what happens at the upstands and outlets, what is provisional and why, who issues the guarantee, and who will be on the roof. Somebody who has thought about your roof can answer all seven from the visit.
This is written to be useful whoever you end up hiring. The questions below are not a trap, and none of them requires you to know anything about roofing: they simply ask a contractor to describe the work rather than the price. A firm that has surveyed properly enjoys answering them, because the answers are where their advantage actually lies.
Which system is going on, exactly?
The point of the question is to move the conversation from a category to a product. "Felt" and "liquid" are families, not specifications, and two roofs described with the same word can be built from completely different materials at completely different prices.
A good answer gives you a system name and a build-up: which layers, in which order, from one manufacturer's range, with the reason that range was chosen for your roof. A poor answer stays generic ("a good three-layer felt", "a high-quality liquid system") and moves on quickly to what it costs. Generic is not modesty; it is the absence of a decision.
What is inside the sheet, and how is each layer fixed?
Because the parts you cannot see are the ones that decide how the roof behaves. On a bitumen system the carrier and the polymer govern how it copes with a deck that moves, and whether each layer is torched, bonded cold or mechanically fixed changes both the risk and the price.
A good answer is specific about both, and explains why: a fixing method chosen for your substrate rather than for the van. A poor answer treats it as detail you would not understand. The differences are set out plainly in types of roofing felt, and they are the four lines that make two quotations comparable.
What happens at the upstands and the outlets?
This is the question that separates roofers, because almost nothing fails in the middle of a roof. Water gets in where the covering turns a corner, meets a wall, passes a pipe or leaves the roof, and those are the parts a quotation is most likely to skate over.
A good answer talks about heights, how corners are formed, whether outlets are being replaced or dressed into, and what happens where the covering meets something combustible. A poor answer is "we will dress it all in". Dressing is what you do to a detail; it is not a description of how it will be built.
What in this price is provisional, and why?
Nobody can see under a covering until it is open, so every honest price for a refurbishment contains something conditional. The question is not whether provisional items exist but whether they have been named.
A good answer puts the certain and the conditional in separate columns, says what triggers each provisional item and what it will cost if it is found. A poor answer is a single number with nothing conditional in it at all, which usually means the conditions arrive later as a conversation on site. How those sums work once a job starts is covered in what refurbishment costs.
What does the guarantee cover, and who issues it?
Two different promises usually travel under one word. A manufacturer may guarantee the materials or the system; the contractor guarantees the workmanship. They have different lengths, different conditions and different people standing behind them.
A good answer distinguishes them without being pushed, names who issues each, and says plainly what would void either. A poor answer offers a long number as though it settled the matter. Most system guarantees carry conditions, including maintenance, which is the subject of whether your guarantee requires inspections.
Who will actually be on the roof, and who supervises?
Because a specification is worth exactly as much as the hands that follow it, and on a small job the person quoting is often not the person working. That is not a problem in itself. Not knowing the answer is.
A good answer tells you whether the crew is employed or subcontracted, who is on site each day, who checks the details and how you raise something mid-job. A poor answer is "my lads". Ask it early and pleasantly; it is a fair question and every decent contractor has heard it before.
How will the site be run, and where does the old roof go?
A roof job happens above people who are living or working underneath it, and most of the friction on a small project comes from the parts nobody discussed. Access, parking, scaffolding, where materials are stored and how the waste leaves are all decided by somebody, and it is better if that somebody is not improvising on the first morning.
A good answer covers the hours, how the roof is reached, whether a skip or a bag is coming and where it will stand, what happens to the stripped material, and what the site looks like when the crew goes home each evening rather than only at handover. A poor answer treats all of that as your problem once the price is agreed. On an occupied building it is not a courtesy question; it is half of what you are buying.
What if the boarding underneath turns out to be wet?
The single most useful hypothetical you can put to somebody standing on your roof, because it is the commonest surprise on a refurbishment and the one that alters a job most.
A good answer describes a procedure: work stops at that point, you are shown what has been found, the revised scope and price are put in writing, and you decide. A poor answer is reassurance that it will probably be fine. The difference between the two is whether a surprise is procedural or financial, and you find out which on the worst possible day.
What if the answers still leave you unsure?
Buy the evidence before you buy the roof. An independent condition survey records what the roof actually needs, with photographs behind it, and every quotation afterwards is priced against the same document instead of against each contractor's opinion.
It also changes the conversation. Once the scope exists on paper, the seven questions above stop being tests and become the ordinary detail of a job somebody is happy to describe, which is roughly how the whole thing should feel. Where it turns out to be a larger project than you expected, the routes are set out in refurbishment options.