I am moving a shed roof attached to a shop with a metal roof and have never seen or dealt with the type of screws holding it down. They have a 7/16 plastic type head attached to the metal screw. The heads are stripping off the screw when attempting to back most out. The head jams in the socket and I am left with the metal portion still holding the metal down. It is flanged with a cross patern type head the plastic was adhered to but fits no tool that I know of and nodules break off in attemp to grab the head with vise grips. Any ideas how to get these suckers out? Appreciative of any suggestions. Thank you.
Here is a photo of a screw and what is left when the plastic head strips off.