The problem with making your own alum wheel getting a hardened rim blank and hardened wheel center and welding them together and having them still be hardened.
Realwheels lists their different offsets on their website and can make custom offsets if you call them. If you get TOO much offset, such as a 14" wide wheel with 3" offset on one side and 11" on the other, it's just going to bend.
Now you can make your own lightweight steel wheels, pretty reasonable.
Diamond wheels will sell lightweight parts to do that.