Corrugated sheet metal roofing


we have about 6500 ft.² of corrugated sheet metal roof that we would like to insulate from outside because we have sound blast that from inside the customer likes the look what is the best insulation and roofing material that we should install, the project is souther california, we have talk to many roofing companies. We are very close to select one. But wanted to find out if anyone has any advice.
We did replace all the damage corrugation from previous roofer. Is anyone has any idea what the budget should be, Also we are very particular seeing screw coming through the ceiling, So we were told hot mopping insulation, And then laying out the plywood we were thinking 5/8” Roof of a saying that says additional $3000 cards which were willing to pay. In addition worth taking building a platform for future conditioning unit.