A prefabricated building structure having a truncated, cone-like sidewall structure fabricated from a plurality of conjoined, arcuate surface sidewall panels with adjacent panels being interconnected by an external interruptible means. The sidewall panels, mounted on corresponding flooring panels, separately support conjoined ceiling panels which are of a wedge-shaped planar configuration and have a truncated inner end flanged upwardly for locking engagement with a central closure means. Various selectable insert panels or modules are engageable within the sidewall panels to provide a structure adapted to a variety of utilities including, but not limited to, housing and storage.