I've been thinking about building some foils (namely a set of daggerboards), but I always stop when I start adding materials costs up. I have the know-how and the expertise to design and build a board or rudder that is the equal of any production board built anywhere, I can even go to the extent of full carbon autoclaved high modulus carbon boards that have CFD and FEA behind them, which is more than most builders do, but they also usually have decades of "this works" experience to backup their laminate schedules. The reality is to build a board or rudder on par with a factory finished board requires aluminum tooling and a great deal of expertise. It isn't something I would try at home with no experience at all. That being said, you can likely hand shape a cedar cored rudder that is the equal or better than a lexan hobie rudder. Net you want the outer profile the same shape, I would run 3 layers of 1" wide uni carbon down the 1/4 chord and a minimum of 3 (structurally likely okay), better off with 6 layers of 9oz fiberglass on the bias around the blade. Assume 0.012" per layer and that should get you the core offset. You could cut the fiberglass down to 4 layers pretty safely if you replace the 9oz fiberglass with 5.7oz carbon, again you want most of the layers on the 45/45 bias.