Very simple, just find an appropriate block of wood, drill a hole for the tang and enlarge it in front with a small file. If you want (and have some basic metalworking skils) you can fashion your own guard and buttcap. Either way, once you assemble the grip it's a good idea to coat the tang with slow setting epoxy to ensure the strongest possible bond. Peen the end of the tang over a tightly fitting washer and you're good to go. Choice of wood is up to you but something like maple or hickory would be a good choice and easy to find. You can finish the wood with several coats of boiled linseed oil. Looks great and preserves wood very well.