Everything I ever built was shaped after sheeting. May try to reread the instructs too. It can be a bit tricky. They should tell you something maybe about beveling sheeting to tuck into leading edge nicely. I've seen that before too. Maybe some indication underlying there somewhere.. For shaping though.. I use a little razor-plane made by "Windsor" company(I think). After you get the hang of that little tool you'll be hooked.. It's very easy, and it takes the bulk off before going to a block or belt, or even hand sand. Good luck.