Back to my question that you did not answer: Have you spent much time in a
totally metal building?
Several years ago I was in an un insulated metal building during a hail
storm. It was noisy beyond belief but remember it was a shop with no
insulation and almost everything inside was a hard surface.
As a kid I helped build Quonset huts with my uncle These were metal roofed
with wood frames, mostly used for machinery storage. I had a chance to see
several of them this last summer and a couple were sway backed. I suspect
condensation has caused rot.