Like was said, first figure out the species. That way you can be use the possible sites in your yard. When picking a spot think of things like existing plants (especially trees and bushes), in a heavy rain does water sit there, when does it get the sun (morning, afternoon, evening, all day, a combination), what kind of soil do you have (can an enclosure be on that soil or will you need to either dig out and add new soil or just have a raised enclosure). You need to think what size you need (keep in mind the need for water, hides, plants, food dishes) and will this be one you can walk in or only work on from outside the enclosure? Do you want to work with wire, wood, cement blocks, or what? How much money do you have to spend on this project? How much of a predator problem do you have? This includes the coons, birds, dogs, ect and don't forget the human predator.