WWFD? (What Would FABO DO??)

Metal roofs............the heater disclaimer MIGHT be because the metal is one roof material that will simply absorb and dissipate the heat. Might not be very effective "but I don't know"

How big are the verticals? Looks to me like they are quite small and sparse compared to the joists. No idea the money you have/ want to spend, you might consider adding some more joists AKA trusses supported by added verticals. It could get expensive.

No idea the snow loads you see, you might plan on shoveling it. FALL ARREST HARNESSES!!! SAFETY ROPES!!!