If those houses are disappointing... I'd love to see what you've got. Those houses are pretty spectacular from my point of view.
Do we just assume there is money enough to hire people to do the maintenance work? - If so I'll go with C as well. I love the fresh outdoor air. - If not it would be D, assuming this is somewhere Italy-based Grrr, Imrahil
I'd learn how to do the maintenance work. I like that DIY kind of stuff and would maintain my treehouse myself (as much as I could)