You need to find a contractor who has a lot of experience with providing roof inspections. General home inspection contractors are generally not suited to this task. The roof is considered one of the most important habitability concerns on most homes. If your local code enforcement officers see something out of whack in your roof, then they can force you to enact costly repairs. Finding an inspector with experience in roofs will help ensure that you don't ever go through this hassle.

Most roof inspection contractors will have a fixed price for their services. You may want to consider avoiding contractors who offer a "sliding scale" price structure on an inspection. If you are asking the contractor to perform some other service after the inspection, then the sliding scale is probably alright. For a simple inspection, you should be quoted a standard fixed price.

Don't hire a roof inspector who comes recommended by your roof installer. Things like this are considered highly unethical since they create an unfair bias in how a contractor looks at your roof. Only hire independent contractors if you want to get a real, solid, trustworthy roof inspection done.