Number #1 needs to be their experience in providing commercial roofing services. 2. Second, repairing verses replacing roofing materials. 3. Types of roofing systems you have experience with, there are generally three: a. Thermoplastic Polyolefin (TPO) single-ply flat roofing membrane. TPO roofing system is a single layer of a synthetic, non-woven material. b. Synthetic rubber roofing membrane application called EDMP (ethylene propylene diene terpolymer). Applied on low-sloped roofs and popular for durability and low-cost. Product available in both white and black, and a variety of widths and thicknesses. c. Traditional rolled roofing materials, shingle, metal and tile applications.