There are two things called a roof survey in Britain and they are not the same product. One is a free visit from a contractor who would like the work. The other is a paid inspection by somebody who will not be quoting, whose output is a written report you can hand to an insurer, a buyer or a second contractor. Knowing which you are buying is most of the value.
The free visit and the paid survey
A contractor's free survey is a sales visit, and that is not a criticism: it is how the trade prices work, and a good one will tell you plainly what the roof needs. What it will not do is give you an opinion with no interest in the outcome, and it rarely produces a document. A paid survey buys independence and paper. Where the question is what is wrong, the free visit is often enough; where the question is whether the contractor is right, or whether a roof has years left before you buy the house, it is not.
Who carries them out
Roofing contractors survey roofs to quote for them. Chartered building surveyors survey roofs as part of a building survey and can be instructed on the roof alone. Specialist inspection firms, increasingly with drones, sell the inspection as the product. For a purchase, a chartered surveyor's report carries weight with lenders and solicitors that a contractor's does not; for a leak, a roofer usually finds it faster.
What the report should contain
Dated photographs of every defect, because when a roof was in a given condition is exactly what an insurer or a buyer's solicitor will ask. Findings separated from interpretation and both separated from recommendations. An explicit list of what was not inspected and why, since almost every roof has areas nobody could reach safely. And urgency graded rather than a flat list, so you can tell the leak from the maintenance and budget accordingly.
Questions people ask about roof surveys
How much does a roof survey cost?
It depends almost entirely on access and on who signs it. A drone inspection is the cheapest because nothing has to be erected; a close inspection from a scaffold costs what the scaffold costs; a chartered surveyor's report costs their time and their professional indemnity.
Do I need a survey before buying a house?
A standard homebuyer report inspects what is visible and safely accessible, which for a roof is often the view from the ground and the loft hatch. Where it flags the roof for further investigation, that further investigation is a roof survey, and it is cheaper than discovering the answer afterwards.
Will a roofer's free survey find a leak?
Often, and quickly, because finding leaks is what they do all week. What it will not give you is an independent second opinion on the repair they then quote for, which is the reason paid surveys exist.