Is there a vapor barrier under the steel roof? Is there any ventalation? Is the steel roof over purlins, or rafters?
If there is no vapor barrier you will have a problem. You can try to install kraft faced fiberglass batts (provided they dont touch the roofing) and cover that with plastic sheeting. Or you could install foam board.
You need to stop all moisture from getting to the steel, this is usually done by installing plastic sheeting over the purlins/rafters before installing the roofing.