Ask for proof of a insurances, licenses, and bonding capabilities before work begins. This will prevent future lien, defaults, and/or Bankruptcy problems from unlicensed and un-insured roofers.
Get several estimates, compare materials and technology. Always keep in mind that the lowest quote is no substitute for experience and professionalism.
Request in writing that no sub contractor be used on your property. This will prevent homeowners liability, Worker injury, and unsupervised quality controlee.
Call and ask for references. Remember, guarantees are only as good as the company behind them.
Take time to visit the contractors office and shop. You should not feel safe if the contractors mailing address returns to a P.O. Boxes or their home.