The thing about building up a BP/W is that by the time you have ALL the pieces, it may not be less than a DSS rig. So, get some idea about buoyancy and lift requirements and look at DSS. I have that rig with an LCD30 wing for diving with a 7/8mm semi-dry wetsuit.
I have also put together a couple of rigs for use with double hose regs. The total cost of the parts has NEVER been less than a complete DSS rig.
But the nice thing about BP/Ws is that you can select parts and pieces from various manufacturers and have some hope that they will work together.
One thing to consider: there are a few wings that will help stabilize the tank and you won't need an STA (single tank adapter). This is clearly the case with the DSS single tank wings. There are some molded-in blocks that support the tank. The Oxycheq and HOG wings have some ridges that do the same thing. Other wings can ONLY be used with an STA.
Another thing to consider is that all wings EXCEPT DSS have the tank bands retaining the wing to the plate. To disassemble the rig, you have to unthread the bands. The DSS wing has 'windows' where the wing can slide over the bands while they are still connected to the plate. The advantage is that you can remove the wing from the backplate and store it separately. I put the plate on the bottom of my dive bag, pile my other gear on top and put the wing at the very top where it won't get damaged. It also makes it easier to rinse out the wing without man-handling the weight of the wing and backplate.
Richard