Should I get a second opinion before replacing my roof?

Not price shopping. The purpose is to test the reasoning: is the roof failing generally, or are the defects isolated? Would partial renewal serve? Is stripping and relaying sound slate an option? Two independent answers to those questions are far more useful than two prices for the same specification.

Ask each contractor to inspect and report before either sees the other's proposal.

Line the two up on findings first: what each says has failed, where, and how they established it. Then compare scope — whether battens, underlay, details, leadwork and drainage are included — and only then compare price.

Two quotations can differ substantially and both be honest, because they include different work. A cheaper figure that omits leadwork or drainage is not cheaper.

A replacement recommended without an inspection report or images. Pressure to decide quickly, or a discount that expires. A recommendation made from the ground or from photographs. A stated cause that does not fit your symptoms.

None of these prove bad faith, but each one means the decision rests on assertion rather than evidence.

The most useful point to arrange a second inspection is before the first contractor's proposal has shaped your expectations, not after you have already begun negotiating on their figure. An inspection carried out independently, without sight of the first report, produces a genuinely separate view rather than a reaction to someone else's conclusions.

Delaying the second opinion until late in the process tends to narrow it into a price comparison, which defeats the purpose. Arranging both inspections close together, before either report is shared, keeps the comparison honest.