The present invention provides a system, or kit, of blow molded panels having integrally formed connectors which combine to form an enclosure, commonly in the form of a utility shed. The corner sections, roof, wall and floor panels are formed of blow molded plastic with integrally formed connectors to interlock with one another. In one embodiment, the ends of the wall panels have locking plugs that are constructed and arranged to fit into corresponding sockets and slide to an engaged position for interlocking cooperative engagement rigidly connecting the components together.