a modular building design includes a building frame construction of superior strength and rigidity with roof , floor and wall panels designed for insertion in modular frame openings . the design permits complete fabrication of all shell components in a central manufacturing facility and is such that the various elements may be shipped or stored in an essentially flat package configuration . the only tools required for erection on the building site are conventional wrenches and nut drivers . the need for skilled workmen at the site is virtually eliminated .