Hi again, Wicked Simmer, I think I know the challenge you mentioned, maybe the "homeless to billionaire" one? I did that one. In that one though they have to have a house, but can't live in it until they make $30k.
Peanuts, what you might want to do is buy an empty lot and maybe just put a bench or something there. If you make a park w/a bldg in it that maybe has a bed or a park w/a tent in it, your sim can "live" there during the winter. Even in the summer, they can sleep in the tent in the park. This is what I did for that "homeless" challenge.