A potential business is building a minimal but livable core house for about the price of a conventional down payment, then building additions as money becomes available to clients. Fashion is also an expensive temptation-one tends to buy too much for the moment and pay too much later. The rectangle both grows well and subdivides well. Complications can develop in time. On the neighborhood level, small lots lead to greater diversity in a given area.
Strong structure is almost universal among long-lived buildings.
Design for disassembly instead of demolition. Drywall screws are a great invention for disassembly. The classic winner in design for disassembly is post and beam. Brand claims they are cheaper, but I have seen studies that indicate that, in use, their price exceeds wood slightly. Also, they are new and untested by time which, by one of Brand's main arguments, means suspect.