I agree with most, at first i would not charge him, it all depends really on how generous he is, and how long he ends up staying, but if he buys some groceries and offers to help, take it,and if he ends up staying longer than you intended him too, then i would broach the subject, my son had a friend move in for about a month, temporarily, and never charged him, he ended up becoming a room-mate in the end,so it all worked out just fine.