Abstract: Improvement in or relating to the prefabrication and erection of building modules including substantially two basic modules: a trapezoidal module and a parallelogram module. Multiple combinations of modules create numerous building clusters that form whole structures that have flexibility of interior wall placement because bearing walls are located at the perimeter of the module. These load bearing walls are all parallel to one side of an equilateral triangle that is oriented on a horizontal plane. Each module contains two or three load bearing walls, and a roof section that spans across the volumes created.