I live outside of Greenville, SC.  3A/4A (technically we are 3A, but I call BS). Our house is literally 675 sqft, single level.  Vented, unconditioned crawl—but we will soon be doing a moisture barrier, sealing the vents, and installing a SantaFe dehumidifier.

I’m currently working on installing a mid-static ducted minisplit and ductwork in the attic, which has gable end vents. 

Current roof structure is asphalt shingles over skip sheathing, with 1×6 rafters.  We will be adding on soon, and with the addition (575 sqft), we plan to do all metal roofing.  

So… the actual question is, what is the proper way to convert the gable vented attic into an unvented, conditioned attic (specific detail drawings help me), and should I wait until we re-roof, or is there a detail/assembly I can do now that will work with the new metal roof, once we get to that point.  

Limitations:  NO spray foam (other than the canned stuff from the box store); this will be used for storage as well-so it is my understanding that I will also have to use drywall as a fire resistant/ignition source barrier?

thanks for the help—I’ve scoured gba forums and the rest of the internet only to find conflicting info, and not much that applies to my specific climate.