[486]
smells things
I always thought the roofs with nails did always leak a little but it was on the order of a few drops per storm, so it'd dry back out pretty quick with open rafters.Back in the day barn roofs were secured with nails that had lead around the heads. They almost never leaked if properly installed, even after a hundred years. The old rubber ones would crack in no time. Then there is proper installation, running the screw down until the washer mashes out is not the correct way. Standing seam will always be "better" with proper installation because the fasteners are hidden. It's also $1250-$1500 a square here.
Because even when nailing on the top of the corrugation it'll catch a few drops in the exact wrong place to get in
also, you aren't mashing that dead soft lead tight enough to seal against the lightweight tin that a cheap bastard farmer woulda sprung for.