To compare roofing contractors, find several candidates, and interview them. Get an estimated price for the job and ask how long the contractor has been in business and what kind of warranty he provides. Ask what kind of underlayment material the contractor uses, how he plans to ventilate the roof and what he plans to do if the deck of the house gets damaged. Based on the contractors' answers, choose the best one.
Ask each contractor for references, and contact the contractor's former clients how well the contractor did his job and what, if anything, went wrong. Ask the former clients if you can come by their houses to see the contractor's work.
While you may receive only the warranty for the materials used in roof installation, good contractors give their own warranties for the roof as well. Hire a contractor who doesn't use synthetic vapor barrier insulation, which may cause the roof to rot. Instead, choose a breathable ventilation system. If a contractor has to remove old materials from the roof before installing a new roof, some of the house decking may get scratched or cracked. If a contractor promises to repair any deck damage for free, make sure that it is listed in the contract.