[AT] OT...Need some advice on old metal building

[Mogrits]

I'm adding onto what's likely the oldest pre-engineered metal building
I've ever seen, much less worked on for a customer. We are going to
re-skin the existing building and add insulation while we're at it.

However, the darned thing is sheeted with dome headed slotted screws
and inside each has a square nut. Removing them is giving my erection
crew a fit. Anyone have a suggestion on how to remove these things or
a quick way to knock the heads off. It being a working building, it's
really going to be an issue trying to get to the nuts when we get to
the roof. We've tried grinding them off and chiseling them off but
haven't found the right way to make some time.

Thanks
Warren