1/8 of an inch thick torch on tar that comes in a roll.
OK, yup I know about it. The guy I worked for called it rolled mastic.
That’s been a problem on metal roofed buildings screwed to metal purlins. Less so metal roofed buildings screwed to wood purlins. Essentially non-existent if you do the labor intensive dob of silicon caulk (or other elastomeric caulk) where each screw is.
One idea I’m kicking around is to build two of them, with a “Dog Run” roof between them to allow for a covered access between the two.