I had a freind who did a lot of rescuing adn fostering who had an outdoor enclosure to die for. It was very sturdy, constructed of 4 by 4's, 2 by 4's and chicken wire. They could get to it through a cat door from the garage. It was very sturdy and ran the length of the garage, about 20 feet, and was about 10 feet wide and about six feet high, and there were platforms of differing heights for the cats that like to perch out of sight. I never had the nerve to ask her how much it cost (since I was raised to believe that sort of question is rude under any circumstance) but I'm sure it wasn't inexpensive. Sadly, she moved to New Mexico to be with her aging, ill mother and had to leave her wonderful outdoor enclosure behind since it had not been built to be portable, and the people who bought her house immediately tore it down.