the roofing module of the present invention is comprised of a sheet of thermoplastic material which has opposed side margins that are bent upwardly at 90 ° with respect to the body of the sheet to provide joinder tabs . the module is formed by transporting a flat sheet of the material between a pair of inwardly - facing radiant heaters which are focused on a line which the sheet will be bent about in order to soften the sheet along that line . after the sheet is softened along the fold line it is transported through a bending section comprised of a series of die rollers which cause the margin to progressively be bent upwardly to the desired orientation .