My friend Tibby has a lovely outdoor enclosure that was made by a company that usually makes outdoor dog kennels. But since Tibby (and his companions) were so very special, they got something for cats instead. It's made of heavy duty frost fencing and is very stable and heavy. There is a door leading to the grounds so Herself can visit or tidy up; it is usually padlocked to keep visitors out. In the summer it is surrounded on the outside by plants and vines, offering shelter, privacy and added wildlife - butterflies.
That's Tibby on the stool by the cat door that lets him go in and out without human help. The door is closed when Herself is not at home and late at night when she doesn't appreciate him bringing worms in for further study. He, of course, would prefurr that it be open 24/7.
To keep the hot sun from burning his tender parts, Herself installed shade cloth (purchased from a local garden centre), made grommets and then attached it to the enclosure with plastic electrical ties. So now Tibby and his friends are shaded from the summer sun.
Herself was able to find a long branch from a tree (some landscaper had cut) and installed it with bungee cords, so Tibby can climb along it. She also installed some heavy plastic shelving to offer additional places of rest. You can see that the summer plants offer interior privacy as well.
Things were kept interesting because of the changes in the plantings over the season and because bugs and butterflies came in and out. And in the winter time, his purrson put up small fairy lights that twinkled on and off in the dusk. Tibby and his friends would gather in the enclosure to watch the light show.