Hey there PDS,
so, the problem w/ answering this question w/ any hard info is that every enclosure should be built specifically w/ it's inhabitant in mind: a boa's habitat will be very different from a lion.
i worked w/ cats for a while, here's what i can offer:
start w/ the basics- makes sure that you're familiar w/ the USDA laws (barrier fences, den size, food storage, etc.), they allow for the BARE minimum, so it's usually a good idea to work up from there.
the strength and size of the cat determined what sorts of materials we'd use; a lion or tiger for example needs chain link, deeper post holes, a food slot, and a large den box. Where as for a serval (60lb jumper) we would use a smaller gauge fencing material and be much more stringent on how many hog clamps we'd use on the roof seams.
you'll also want to consider any sort of plant life that may be inside of the habitat- make sure it's not toxic for whoever your housing (ie: tanzy weed & horses); plants are also a great form of enrichment- lots of trees made the leopards happy for climbing; on the flip side, no sapling could survive the tigers scratching & peeing (they sure had fun killing them though!)
there are just soooo many factors involved in answering a question like this; and of course budget is a big one as well...
a few little things to keep in mind: makes sure that you've got easy access to a water source (it's not fun hauling 5 gallon buckets of water 3/day a 1/2 mile to refill your buddy's water. Safety first- if you've got an animal that is any sort of threat, have a double gate system (this is a good rule of thumb for most exotics, but may not be needed w/ some of the smaller, slower guys). It's generally a good idea to be as familiar as possible w/ the species- what is their natural habitat like? how can you create the feel of that habitat w/in the space that you have available?
hope this helped, please feel free to email me if you have any more questions; and happy building!