The present invention includes a system or kit of injection molded panels and other components having integrated connectors which combine together to form an enclosure, preferably in the form of a gazebo. The support posts, roof rafters, roof supports, roof panels and walls are formed of injection molded plastic to interlock with one another without the need for separate I-beam connectors. The system incorporates a minimum number of components to construct a gazebo type enclosure by integrally forming connectors in to the injection molded components and panels. This minimizes the need for separate extruded or molded connectors to assemble the enclosure. The symmetry of the support posts, roof rafters, roof supports, roof panels and other components also minimizes the shapes of the components and simplifies construction of the gazebo.