Motts mentioned earlier that they were copper.

"It looks like this was originally the tuberculosis hospital; one building with two extended solariums on each side, which create terraces on top for fresh air treatment. The copper roof is pretty unique"

http://jacksontn.clubw....com/DianneODell.cfm

Check out this link. I believe the article helps place another perspective on these machines. Hope you all have the opportunity to check it out.