When I shaped my first few this summer, I used pink insulation foam from home depot just to figure out how to shape rails and how to use all the equipment. A 8' by 2' by 2" piece costs 35 bucks and shapes just like regular eps foam. I started by making a planing hull shape, essentially a really big bodyboard with no fins, meant just to go fast and use a lot of the rail to turn.
I came up with a template for the outline one side on a piece of wood, then traced it onto both sides. I cut the block of foam down to roughly the shape that I wanted with a saw, and then used strips of sandpaper attached to 2x4s to trim down to the exact shape that I wanted. For rails, I measured out the bevel of the rails (in my case 1/8 of an inch because I wanted them to be hard), and drew the distance on either side of the board, then sanded to the line with my blocks of sandpaper and mellowed out the edges by running a piece of sandpaper across the rails to round everything off. I didn't end up glassing it, because I just wanted experience shaping and you have to use epoxy resin to glass the pink foam, and it's ridiculously expensive. I had so much fun shaping it, the board ripped, and I'm working on shaping more as we speak.
Hope that helps.