Suppose we build a home that is only a big empty room, 2240 square feet, as shown in the diagram on the upper left.  Plumbing fixtures for a kitchen and two baths are clustered near the center; the outer walls have regularly-spaced windows and doors; but the rest of the space is empty except for a grid of soffits hanging down from the ceiling to break it into four-foot squares, with little sockets set into the carpet every four feet. We give the homeowner 50 or 60 columns that will fit into these sockets, plus a couple hundred insulated metal wall panels (some with doors in them) that can be bolted onto the columns.  With some planning and about a day's work, he can use these columns and panels to erect interior walls wherever he wants.  If need be, he can even change his home's floor plan from week to week. The diagrams at center left and lower left show only two of the possible layouts.