Need help restoring an old railroad caboose

[runaway_train]

I'm gonna restore a 900 series caboose and have to strip it to the bare steel frame. I'll make sure that I sandblast, weld, and then rebuild everything to its original form but I don't really have records to refer to. This is my first time doing it. There's gravel and tar paper on the roof but looks like it was added years after buying? Doesn't seem original to me. I just need to know what's the original roof material. Hoping you guys have some ideas.

 

[Free Beer]

The original roof would very likely have been a canvas covered wood. the canvas I think was stretched over the wooden roof boards. and then sealed with a waterproof paint or something like that. The gravel and tar paper you see were added later for better waterproofing.

 

[YardDog]

Thanks for the info! Using canvas over wood with waterproof paint sounds smart for early roofs. Do you happen to know what type of waterproofing was usually used? Was it pine tar or something else?