A novel composition of materials that can be extruded into sheets to form panels to create a roofing system wherein the panels are formed to interlock with like panels in order to provide a substantailly weatherproof covering on a roof. The sheet member has a top layer made of ASA (Acrylonitrile/Styrene/Acrylate polymer) and a bottom layer made of PVC (polyvinylchloride). The two layers are extruded and bonded or preferably coextruded. Then the bonded materials are thermoformed to resemble more popular types of roof coverings such as shake or shingles or tiles.