Abstract: A transportable form structure for use in making a building. In accordance with the invention modular interlocking form blocks are stacked on a base frame and then secured so that the blocks do not become dislodged when encountering stresses during transport. Preferably the blocks are securing by applying a vertically directed compression force to the walls of the structure about the periphery thereof. When the form structure is completed, it is both strong and light weight. It can be lifted onto a vehicle and transported to a location of installation. At an installation location, the form structure is secured to a foundation, and filled with a filler material such as concrete.