You just never know where someone might be living.
Case in point... Police in Antioch recently found a person camped out on the roof of a BART station.
They only located the individual after a BART passenger spotted someone lowering a bicycle from the roof. Were it not for that chance encounter, the digs may have gone unnoticed for who-knows-how-long.
While it looks like a well-assembled camp, I don't think it would have held up very well in the rain.