Building Casita/tiny home in voc

My wife and I have been home shopping. We put an offer on a house with Casita , it's a bit of a fixer upper but the inspection came back needs a lot more tlc than we wanted.

So we looked up at 2 homes in West Sedona which isn't my preference that already have them. Then today a nice home popped up but doesn't have a Casita but would be perfect in voc.

Soo long winded question , how hard would it be to add a Casita or tiny home in our yard. Fwiw this is for friends and family to stay