Abstract: The method of constructing single story building structures involves installing upon a prepared ground surface an array of upstanding load-supporting columns in spaced parallel lines and transverse parallel rows to define bays between adjacent column lines and define a rectangular panel area between each group of four columns at the corners of each such area. Primary and secondary panels are assembled in the panel areas at a convenient working height near the ground surface with the primary panels to form the roof structure over alternate bays and the secondary panels to form the roof structure for the bays intermediate these alternate bays. Each primary panel includes beams of a length to extend between adjacent columns in a line of columns, the beams being located at each end of the primary panel, and spaced joists secured perpendicularly to these beams with joist bridging secured perpendicularly of such joists.