I like FLU’s charge him rent and then give it back to him when he moves out idea. Don’t tell him about your plan. Then if he uses his time to get his life together, that will be a nice head start on his future and if not it will give him enough for first and last month’s rent, etc.
Remember that no good deed goes unpunished, so plan on him being completely ungrateful and perhaps even pissed off at the end of his stay. It’s a kind gesture, though. Stick to your rules. You’re not doing him any favors by enabling him in not growing up.
