I would also build a house, but one that encouraged physical activity. For example, it would have to be a tree house, so the only way to get in or out is to climb up or down a rope. Not a rope ladder, a rope. Doors slide up and down, and have to be manually opened using a series of weights and pulleys that work out your arms and legs. Electricity is provided by solar cells, but also by a pedal-powered generator. In order to watch television, you'll have to keep pedaling. In order to get from one room to another, you either have to walk across a foot-wide balance beam or get across using the monkey bars. They're far enough apart that you'd have to be the tallest person in the world to reach both comfortably. Of course, there would be safety nets underneath, but they only lead back down to the ground. You'd have to climb back up the rope again.