A commercial roof can be a traditional pitched roof comprised of shingles, slate, or tile. But we typically think of commercial roofing as a flat roof system. Flat roofs are most commonly covered in BUR or Built-up Roofing, Metal Roofing, Modified Bitumen Roofing or Mod-Bit, EPDM or Thermoset Roof Membrane, and TPO Thermoplastic Roof Membrane, also referred to as PVC.