My HO scale modular club has hexagonal corners, and they nest together, get bolted together, and then get put in the club trailer for transport. The yard, power supply, throttles, and corners stay in the trailer, and are owned by the club, so that if someone is sick, we still have four corners. For this same reason, we have 4 foot duckunders, and we can have mulitple duckunders if someone with a 4' module doesn't show up, and there isn't an extra. A few people have corners, but I have never seen any of them. We use the club-owned ones, as they are light and durable, and easy to set up/ transport. If you want to build with a nonstandard shape, as long as the dimensions are the right size (4'x4' typically), and track and electrical is to spec, it should be fine. Just don't make it 5x5, as then there will be two 1 foot gaps somewhere in the layout.