I'm talking mobile homes and an area with an average home value of under $100k. One of the big selling points of metal roofing here is durability, i can point to another neighbor (3mi down the road) whose house was built sometime in the 30s but is now a more valuable redneck shotgun shack because of the (burgundy) metal roof. Edit: come to think of it, it may have been tin roofing originally; it had been shingled before the metal tho.

It sounds like your area is one where the location and the market determine value far more than anything on the land, so treat it as "build to suit" commercial property and assume anything built on it is disposable.