Looks like there was no real support, like a wall, in the center. Was the roof just resting on the roof over the boxcar? When you rebuild the roof, get an engineer to design a real roof system to avoid this in the future. You're fortunate there wasn't any more damage than there was.

Later!
Mr. Ed

It looks like the rafters were OSB I beams. It also looks to me that there may have been insufficient lateral bracing between the rafters. With the heavy snow load all it takes is for one of those beams to deflect sideways to start a cascade failure.

I would be very interested in learning what the assessment was of the cause of this failure, aside from the obvious heavy snow load. What part of the structure failed first?

There were a number of problems, starting with the fact they used floor joists instead of roof trusses. Combine that with a very large flat roof that from what I understand has leaked the last 10 years of it's 20 year existance. I saw a lot of rotten wood laying on the ground, which was the lateral bracing. What it looks like is a bad design and cheap materials. There's really no excuse. The roof is laying on top of the box car, caboose, and the Pullman. The tricky part will be getting the parts that are still hanging down. We've got a crane, but it's got a couple of hydraulic hoses that need to be replaced first....