I have 3 formerly feral cats who really want to be outside, but I can't let them run loose or they will go back to the old neighborhood. I would like to build them an outdoor enclosure in my backyard. I'm thinking 15' x 20' x 6' with room for a little pond and some things to climb. My biggest problem is that my back yard slopes down from the house. The only window I have to use for there exit/entry would be as high as a second story on most houses. I need to connect this to the enclosure so they can't escape. Has anyone done a project like this? If my yard were flat it would be so much easier! Thank you.