A shell roof for a gasline station in Michigan, was formed by a technique using foamed plastic planks supported by stressed wires instead of conventional forms. The technique is as follows: (1) concrete tie beans are cast in form of X to connect piers and restaint outward thrust of the shell. (2) Wires are strung form center ridge to edge beams where they are held be prestressing clamps. Planks of foamed plastic are placed over wires with staggered joints and "H" clips to facilitate twisting into double curvature. (3) Wires above planks are 2 feet apart, streesed to 400 pounds per wire. The wires warp foamed plastic planks into hyperbolic paraboloids. (4) One half inch layer of cement mortar is brushed over surface of shell to provide stiffening. (5) Lightweight aggreagate concrete is placed over the shell quadrants. (6) Latex modified cement plaster was used to finish the underside of the roof.