Every once in awhile, someone asks me about putting metal on a roof that is either round or else has concave or convex curves up the rafter like a bell shape.
Vertical seam panels, unless hand-formed or customer curved, do not work real well on concave or convex surfaces. On a round roof, standing seam panels can be used but they must be tapered.
For many of these roofs, the best metal option is often a small in size modular shingle style panel. They usually work very well on bell shape roofs but can also often be hand formed for round roofs.
Feel free to send me pictures of your roof and I will give you ideas!
It is interesting on complex roofs that the building owner faces high labor costs regardless so it makes sense in many respects to choose as permanent of a roof as possible and avoid future re-roofing costs.