FlyNFish44 was right. CHuck Cunningham's article in Lindy's website is the defining document for getting started in float flying.

If you don't want to make them from Foam (Recommended. Never leaks), you could Use chuck's outline, and build the floats like a sheeted fuselage, with ply bulkheads at the mounting points for the struts. If you want to be adventurous, make the bulkheads in an inverted pentagon for V-bottom floats. About 15 degrees of V and 15 degrees of tumblehome in the sides works well. Reinforce all the edges with a stringer/keel. Just keep them light.