Does he have Insurance .
How long has been in Business .
Gives you Reference on past Roofing work he did.
Be sure, if possible, to inspect previous projects rather than going based on a recommendation. Unfortunately, it is easy to ask a friend or relative to falsely promote your business. It is important to verify any license required for a roofer in your state, and do a quick internet search to see if there are any red flags before hiring.