I built one a while back. Made the harness, hardware, and used a deco SM bladder. Perfectly fine for al80's or LP 72s. My 75.5s are too heavy for it. Randy at Piranha has all the hardware plus some neat little items that you won't see anywhere else to customize it.
He can also supply the webbing and bungee so other than the wing itself, you don't have to go anywhere else to get all the bits for it.
I will say this, if you are not already a sidemount diver with experience in different rigs, building one from scratch will not be easy. There is a lot to consider to get it right.
Before you build one, buy a used rig, take a class from a proper SM instructor, not some dimwit that got the instructor card after a weekend workshop on one rig, and get a hundred or so dives in.
That will make it much easier to build your own rig.
I have built three using a simple harness with the deco bladder, a modified HOG TBCS harness with an XDeep Classic wing specifically for heavy steel cylinders, and one for playing around with al40s and no bladder. Just using lung volume and proper weighting for shallow dives in a wetsuit.
I've also taught in or used HOG, Manta, Dive Rite, Hollis, and X Deep harnesses.