Using my flat truss module, connects 3 trusses in an equilateral triangle, creating a 3-D truss structure. Imagine 3 two dimensional truss structures connected in the shape of a triangular prism. Conceivably could create any shape if it could be made from rectangular pieces. Boxes,tubes with various numbers of sides, arches (with a little help)...

EDIT: Integrated qharley's changes to better space the diagonal supports.

In the openscad file: The space_truss() module takes a length and width (all three sides being the same width) and the diameter of , and creates, well, a space truss. For larger trusses, you could simply multiply the formula for the number of segments made by an integer. Or just set segments equal to an integer and experiment. The default was chosen because it looked to be appropriate for an idea I had to replace threaded rods in my RepRap Prusa with printed parts.