The first step: Read about floating things and join a boat building forum. The choice was BoatDesign.net and here was my first posting: http://www.boatdesign.net/forums/boat-design/starting-scratch-houseboat-50629.html Insights of the first approach: There seem to be–generally speaking–two ways to build the hull: pontoons and scow. Pontoons are… well, pontoons. Scow is a box and the floating principle is much like what you find when you put an empty bowl in a tub full of water… it floats. The consensus seems to be that the scow approach is cheaper and easier–particularly for a beginner. So it seems that it will be scow. Now, instead of worrying how big the hull should be, I will start by designing the house paying attention to keeping the weight down. Ultimately, I hope that it will be easier to figure out the size of the hull for the house I want than the house I want for the scow I thought I would build.