Lots of views, fresh air if possible, warm spots for the cat to sleep and more than one, some place with either wildlife and/or human activity, and of course scratching pads/tower.

Granted, I do all of this and my cat (a gift from the pandemic someone dumped on the side of a mountain for me to find, despite not wanting to be a pet owner, thanks humans!) still manages to find a way to sleep on equipment I don't want to have to replace...

Edit: typo

Go vertical if you have the room. Put in lots of ramps and places to perch. They like grass and small plants.

For construction, we did a two by four frame with welded wire covering it. The welded wire is very secure but still allows a nice view, and is pretty cheap. If you have a Tractor Supply store near you in US) they have it.