The H4 and the H5 shotguns aren't that different from each other (I think the only difference is the flashlight on the side). I would say though, like Peter said, using a Nerf gun for a base then mod it using foam, PVC or wood. I wouldn't buy a brand new NERF gun though, check out a pawnshop or a goodwill they could have some for a good price. Also, just look around on youtube and/or forums here some tutorials I'm sure at least one exists.