Why can two roofing quotations be very different?

The most fundamental difference is what each contractor believes is wrong. A quotation to renew a valley and a quotation to replace a roof are not competing prices; they are competing opinions, and the useful comparison is of the evidence behind them.

Ask each for the cause in writing, with images. Where they disagree, further investigation is the sensible step rather than choosing the cheaper opinion.

Underlay type, batten grade, ventilation provision, leadwork, ridge and verge system, disposal, and access all vary between quotations. Any of them can move the figure substantially, and omitting them makes a price look competitive while shifting cost into the future.

Timber allowances are a common omission: without one, additional work becomes an extra once the covering is off.

Business overheads, insurance, guarantees, whether the work is subcontracted, and how long the contractor expects to be on site. A firm carrying proper cover and standing behind its work costs more than one that does not, and that difference is worth paying.

None of this means the higher price is automatically better. It means the comparison has to be on scope first.

Two quotations can also differ in what follows completion: the length and terms of any workmanship guarantee, whether a written report or specification is provided for your records, and whether the contractor remains contactable if a query arises later. These are not incidental extras — they affect what recourse you have if something needs attention after the job is signed off, and they are worth asking about directly rather than assuming they are equivalent between quotations.

It is also reasonable to ask each contractor how they handle a defect that appears shortly after completion, since the answer reveals something about how the price was built. A contractor confident in their specification will usually describe a clear process for addressing genuine defects, whereas vague reassurance without detail is worth treating with some caution when comparing otherwise similar figures.