The present invention relates a low cost, highly insulated light weight prefabricated building assembly capable of providing a swift, efficient and economic construction of exterior walls, interior walls and roofs to form a sturdy building assembly. The present invention includes a plurality of exterior wall panels; a plurality of styrofoam exterior connection blocks; the plurality of exterior connection blocks being capable of joining the plurality of exterior wall panels that form an exterior wall of the building; a plurality of roof panels, where the plurality of roof panels form a roof of the building; a plurality of interior wall panels; and a plurality of interior connection blocks. The plurality of interior connection blocks are used to connect the plurality of interior wall panels that form at least one interior wall of the building.