Alan- The location was a government office. Everything you see was concealed above a suspended ceiling.
The wood joists are actually 2x12's (actual measure more like 1 1/2 x 10 1/2 inches) used as rafters to support the roof.
To the right, you can just make out the solid wood blocking, used as lateral bracing between the rafters.
It's not obvious in the pic, but there is a significant slope to these rafters. Let's just say that this "flat" roof has enough slope you don't need to worry about water forming puddles!
The "plumbers' tape" is galvanised steel, of a gauge just a little too heavy to be easily cut by your diagonal cutters, but easilt cut with aviation snips. (Maybe 18 gauge?)
