Metal roof under concrete porch

I have a room in my house that is directly under my concrete front porch and the concrete is sittng on a metal roofing. This room is constantly damp and has the standard "mildew" smell associated with it. The walls in the room are concrete and sealing those is no problem but I need to stop the condensation in the room. Based on what I've been reading, the spray foam insulation seems to be the way to go but with temps in my area dipping all the way down to 0 deg and below, will that be sufficient barrier? Is there any prep work I should do to the metal roof prioring to getting it applied? Thanks for any guidance you can provide.