I've built a couple of spare tire carriers but I don't have blueprints for them. I just get an idea of want I want, make some simple sketches with some measurements, and start building. I design as I go along. My first one swung out like most of them do. My second one I have on now folds down so the back of the spare tire turns into a table.
Figure out what type of material you want to use and how you want to mount it to the Jeeps rear cross member and go from there. This is what I did. After you get the basic bumper mounted, have someone hold the spare in place above the bumper and take some measurements. Use beefy enough material so it will support the load, but light enough so it won't add too much unnecessary weight.
One more note. I've been a machinist/welder/fabricator for about 20 yrs now. It pays for me to build my own stuff because, 1. I have the know how of how to do it, and 2. The stuff I build is usually one of a kind and you can't find it anywhere. If you guys have the know how to pull this off, then I say go for it. But for most people, it would be easier and cheaper to buy aftermarket.