When soliciting multiple proposals, be sure you are comparing apples to apples.  You may think you are saving money upfront, but in reality the materials, workmanship, or warranty are coming up short in the long run.

Four (4) items to check your proposals for:

1. Materials to be used (as required):  sheeting, underlayment, metal, roofing material, vents and ridge, etc.
2. Warranties:  workmanship and material.
3. Liability Insurance:  This protects you and the contractor; and, unfortunately, it's one of the first expenses cut by depressed and failing businesses.  If you are not sure, ask for a copy of the certificate.
4. Payment Terms:  be sure you understand what you are responsible for and when.