To follow are some photos of our recently completed Cat-patio.  Our house has a corner where we were able to use two existing walls and just add two sides and a top to enclose it. We built simple frames with 2x4s and stapled wire fencing to the frames.  

The roof is also framed, but 2x6s give it better strength and bulk to hold a sheet of corrugated metal as our cover. We bought a pre-made wood screen door, handle and latch set. We mounted a couple of Catswall CatCubbies to the exterior wall.  The Cubbies are intended to be used on the floor and indoor, so we had to drill mounting holes to adapt them as wall mount boxes.  A coat of blue exterior house paint will help protect the pine wood from the outdoor elements, since we are using them for outdoor use. A pre-fabricated cat door is set into an existing  window, allowing our cats to come and go as they please! A CatsLadder and some CatsPassages finished off the vertical playground and our cat Surmi now has a fun, safe, outdoor area to roam.