Odin the Western Screech Owl (Megascops kennicottii) had his indoor habitat, but he needed a place to watch the birds and get some sun. We had a tight fit on this one, and wanted to maximize every inch. We put the vestibule in the narrowest spot, and left space to fly at the opposite end.
Raptor habitats (called mews) can't be crowded. They can break a feather (can be disastrous) or get entangled with their safety equipment. They are also reeeally messy eaters!
Cleanable interior walls and removeable perches with variable sized and materials to prevent bumblefoot
Windows with doors that can be left open or closed as weather allows
Screen to prevent mosquitoes as well as dowels for bars to protect his talons if he decided to fly against the window (and to protect him from local cats)
Clear roof to allow natural light (ideally should be replaced every few years as the material can get brittle)
Mesh covering the underside of mew to prevent rodents from damaging wood with nests
Safety vestibule also has shelves and hooks for cleaning supplies
Enrichment, of course!