Abstract: A method of building in which building units are made in a factory the building units having lengths and widths arranged in two directions as a horizontal modular grid and so that the center line of any joint between any assembly of two or more building units coincides with any selected grid line of the modular grid. The units are transported to a building site and assembled in a building cluster with the building units removably affixed to each other and to foundations, the completed building cluster having roofing thereover and joints between units having covers thereto.