A recently introduced system for fast erection of low to middle price range concrete homes features a mobile casting unit that is rolled onto a prepared concrete foundation slab to cast the concrete for three exterior walls and a roof in a single continuous pumping operation. Within 24 hours this mobile unit can be rolled away and other forms set in place for casting the fourth wall. By the end of the second day the house is enclosed and ready for addition of interior walls and completion of plumbing and electric connections incorporated in the foundation slab. The structure can be occupied within a week after casting of the foundation slab. When the previously prepared foundation slab has cured long enough to provide adequate strength, the interior form assembly is rolled into position and stabilized by means of jacks. Positioning of forming sections and their subsequent removal is facilitated by hinges on the sections. The exterior form assembly consists of five sections which provide roof eaves and outside surfaces of the first three walls. Wall and roof reinforcement mesh is set in place before positioning of the exterior form assembly. Precise setting of these forms is accomplished through a system of J-bolts cast into the edges of the foundation to serve as mountings for the form supports. Prior to casting activities, insulating tongue and groove planks are laid on the hinged roof grids to provide the surface on which the concrete roof is cast. The insulating planks also serve as the finished ceiling inside the shell. The walls and roof on the tree sided concrete shell are keyed to receive interior and exterior forms of the fourth wall. These forms can be positioned and the concrete placed on the second day as soon as the mobile casting unit used the first day has been removed. Concrete is placed through ports in the roof to make the fourth wall an integral part of the shell.