drying roof sheeting in attic.

Hi
got called to give an estimate on remediating mold in an attic. Got there and the roof material was glistening. Put the meter to it and its all wet. Its not rotten or anything like that.
What can I use to heat up the area to dry it out? Its 20 degrees outside.
the opening to the attic is small very small. Its gonna be hard to get a decent sized dehumidifier up there too.