Soldato
You need proper tech screws we use on site not retail stuff. Most cladding and roofing is fixed to steel frames like this it's nothing unusual.
https://www.google.co.uk/url?sa=t&s...PrTk8B2_GcxV3PTxg&sig2=esJWFrrIrYdRpm7szVqerQ
It's a bit sad, but discovering these made me happy.