Each state has it's own version of a mechanics and materialmen lien law. These laws allow a contractor or material provider to lay claim of lien on your property if labor and materials are not paid for!
To prevent this potential problem -- ALWAYS require your contractor to present you with a Final Wiaver of Lien from both himself and any material supplier that delivered goods to your roofing project. Do not accept any excuses or believe that these documents "are not needed". Doing so can put yourself in a position of having to pay twice for your roofing project. This is an area of construction law that many property owners are unfamiliar with.
Specific State laws can found here: