hi lill/ Robert? a contractor has done all the ground work, we just don't have the access to machinery to do that but OH and his helpers are fixing on the roof to save some money.
They are using Tek screws supplied by the roofing company these self tighten i believe
but i'm a girl so a bit ignorant on those sorts of things, but he did say something about pre- dilling the sheets first with the bolts supplied, so i think that means they self drill. OH is currently fast asleep on the sofa in front of fire, sensible man, so i will find out a bit more when Sleeping Beauty awakens