Abstract: A building assembly for efficiently and economically constructing walls, roofs, and floors for a building assembly that utilizes a prefabricated building panel made essentially of a plastic foam core with a thin coating of plastic resin or acrylic and portland cement applied on each side for structural rigidity, the building panel having a standardized semicircular recess disposed about its perimeter for receiving pre-sized, cylindrical connectors also made of foam with a coating, and half-round connectors that connect the panel to a slab, and that also fit in the horizontal perimeter recesses of each panel. Each building panel also includes vertically disposed parallel voids that are 4 in. in diameter, spaced 2 to 4 ft. apart, that receive poured concrete or rigid piping to provide structural rigidity to the entire building assembly. The poured concrete includes rebars that are tied to the slab and are used to tie to the roof. The building panels may be used for walls and are 24 ft. long, 4 ft.