@TriTri Is your cat pen going to be attached to the house or accessed via a tunnel with cat flaps ? not that it really matters, I'm sure one exit/entry will be enough. One thing to remember to include is an airlock system so that you can enter the run without any chance of escape. I used to think that Meeko wouldn't use outdoor trays but as you will see from my reply to @Psygon I was mistaken and made to look like prize numpty when I thought he was constipated. I agree lighting is a must , Meeko has 2 static floodlights down one side of his run mounted on the garden fence and a sensor motivated one at the end of his tunnel as he likes to sit out in the dark especially in warmer weather but me being paranoid I need to know he's okay Also in the winter months it means his time outside isn't limited to daylight hours. If there is anything else I can help with give me a shout .