The 1st thing I’d advise, is to make sure your friend doesn’t live in a homeowner’s assn that has CC&Rs which might cause a problem. I have a friend here who put a cage on his own property, and ended up getting fined $100 a day until he removed it. He ended up putting a strange concoction in his garage in order to pacify the old bluehairs here. Musta worked though. If you watched Or St in the last couple weeks, you saw his kid.
As to where to begin, I wish I could help, but I’ve seen literally hundreds of different setups in the last 10-15 years, and they all seem to work to some degree. A lot has to do with how much $$$ he’s willing to spend, and how much room he has.
I wish you and he all the luck in the world!