Abstract: A factory manufactured building assembled on site, comprising a load bearing structural frame with exterior wall units, floor units, and roof units supported thereon. The various units are assembled on the structural frame using a method that allows simultaneous assembly, or assembly in any desired order. The wall units are installed using devices which expand into the structural framework. The roof units are installed using devices which clamp onto the structural framework. The floor units rest on ledges formed in the framework and are secured thereto with clamp devices. All electrical, plumbing and mechanical systems are installed in the various floor, wall and roof units at the factory, and are connected together at the site.