I've bought all mine ready made, but a friend of mine put a very nice one together from PVC pipe and doe skin; threaded a couple dozen lengths all the way through to knot at the hilt, and wove more around the handle, with a heavy weight for proper balance.

As far as advice, I would probably cut the dowel in half and sandwich the belt between those with several screws (be sure to pre-drill and inset them), and buy some fabric or poly for a comfortable grip. Either fray the belt for a cat or leave it whole for a heavy whip.