Abstract: A prefabricated building of symmetrical polygonal shape secured onto a concrete slab and symmetrical about a vertical central axis, the building having vertical columns in each polygonal corner and the columns being joined by perimeter beams extending therearound parallel to the slab to form a substantially closed main framework. The building further includes roof beams supported entirely by the columns and extending diagonally upwardly and inwardly to an apex member which joins them. The columns have connectors attached to them to receive the ends of the perimeter and roof beams which comprise two C-shaped members disposed back-to-back with their webs slightly spaced by internally mounted spacers. Prefabricated side and roof panel members enclose the framework, and are made thick enough to hide the beams and the columns and to lap each other to form an inclosed structure.