Metal roof on a cement block backyard workshop

I'm building a 10' x 14' cement block backyard workshop that needs to be fire-resistant so I can't use any flammable materials.
It will have a shallow slope roof (3/12 pitch).

1- If I attach vertical metal panels directly to a series of galvanized metal rafters with NO underlayment (No plywood or waterproofing membrane) will the metal roof still provide an adequate rain & snow barrier?

2- Can I finish the roof edge with just a simple "drip edge" attached directly to the cement blocks all the way around the building? The top row of blocks will be filled solid, so I could screw in the drip edge.
I don't want to use a wood fascia board (flammable), and I don't plan to use soffits or rain gutters.

3- Can I place mineral insulation (like Roksul) directly underneath the metal panels (fitted between my metal rafters) to give it some sort of "sound barrier"?

Thanks!

I'm planning to use galvanized roof rafters that are intended for use with 10'x14' sheds made by Arrow.
Arrow sells "beef-up kits" for running extra full length rafters in their standard steel panel roof sheds, in order to support the extra weight of snow during the winter.

They are C-channel style 1"x4" beams and they can be sandwiched and bolted back-to-back to make them into "I-beams" for even more strength.

I figured that if a company sells them for the purpose of building their own steel panel sheds, I can't go wrong in using those :)

Todd, I called them "rafters" but these C-channel roof rafters actually run horizontally the whole length of the shed. So they are basically "structural purlins" so to speak.
You just bolt these C-channel "rafters" to heavy-duty angle pates that are bolted into the end walls of the shed.
That way, the tops of the "rafters" sit flush with the tops of the walls.

Thanks Todd and Eric!
I really appreciate the quick responses.