A building module for housing purposes comprises a rigid, rectangular, three-dimensional truss formed with four steel end columns and steel beams extending between the columns. Each module includes a floor panel extending between the four end columns, wall panels, and a roof panel extending from two of the end columns, parallel to the forward column and terminating a spaced distance from the two end columns. A first rectangular folding panel has one end hingedly attached to the edge of the roof panel termination and a second rectangular folding panel, larger than the first rectangular folding panel, has one end hingedly supported between the two end columns. The first and second rectangular folding panels may be folded into positions parallel to their roof panel with their edges overlapping to form a compact module.