I had The Elements of Computing Systems in my lap, opened to the chapter on creating an ALU as i came across this post :) Still have to build all the logic chips before I can implement the ALU though. This stuff is super fun.
Actually, you don't need to implement the other chips to create your ALU. You just have to implement the chips in the chapter. Each chapter is designed to be self-sustaining, so if you wanted to jump ahead to make the ALU you could, then later implement the underlying components.