Salam Aleikom wa rahmatullahi wa barakaatuhu Ustadh is it permissible to ask for money on behalf of a man who cant pay rent?

Yes. Collecting help for someone in need is praiseworthy, and asking is allowed for the one who truly lacks what suffices him. If you decide to ask, then ask in proportion to his need, without insisting or pressing people, and in a way that leaves no suspicion about where the money goes.