I made my Hound helmet by sculpting an original out of oil-based clay, then creating a mold with platinum silicone rubber, and then cold-casting it with Colormatch 325 plastic resin with nickel-silver powder added. I've yet to make the under-helmet and the plating that goes around the neck. The techniques of sculpting and casting are fairly straightforward, just time-consuming and possibly expensive if you screw up the casting. I suppose the helmet could also be made a bit more cheaply with fiberglass and bondo.
Oh, and for the leather armor, I riveted overlapping strips of 8 oz shoulder leather with medium-sized antique nickel rivets. I aged the rivets with an acid steam bath to make them look less shiny-new and more old and ugly. I would recommend using a thinner leather than the 8 oz because it creates a very stiff garment in the end. My armor has about 6000 rivets in it; again, it's very time-consuming to make. I bought a wholesale discount card at Tandy Leather to save about 40% on my purchases, but the armor still cost me about $250 in materials. I've seen some people use 3d fabric paint on upholstery leather instead. I don't really care for how that looks, but it is an alternative option.