The original roof was terne metal, a soft iron (later steel) sheet which was lead "washed" (later zinc washed) both to protect the metal and to make soldering easier. I believe that terne was a cheap substitute for copper roofs.
Railroad roofs were composed of sheets (roughly 18"x24") of terne, with folded locking seams which were rolled, then soldered.
The last maker of terne went out of business about 10 years ago. Their equipment was purchased by Revere Copper (as in Paul Revere, the colonial Boston copper smith who made the "midnight ride" to warn the "country folk" that the "British Are Coming" and led to the first battle of the US War of Independence)
Revere now offers two "terne" products, one zinc on stainless steel... which is too stiff for traditional railroad roofs but works for standing seam roofs, the second a zinc washed copper. C&TS used the copper product on the restoration of coach 292. I believe that it was recommended for use on the Tourist Sleeper by C&TS restoration staff.
Dan Markoff is using galvanized sheet with locked soldered seams for Elsa...
Randy Hees
Randy Hees
Director, Nevada State Railroad Museum, Boulder City, retired
PacificNG.org - a curated Wiki on Pacific Slope Narrow Gauge www.pacificng.com
Moderator - Railway Preservation News www.rypn.org