Thanks for all of the thoughts on this so far. I was thinking along the lines of a mail and baggage car. In "Rio Grande Narrow Gauge Varnish" on page 55 there is a photo of the end of car 66 in the car shop. The car is receiving extensive repairs and you can see the substantial header above the end door. It is rounded on the ends and flat in the middle where the clerestory structure sits. It also has the beams that stick out a little ways beyond the end wall. It is probably just me dreaming but it would sure be fun to take a closer look at this structure.
As others have mentioned the peaked roof looks like a flimsy cover added later. The structure underneath is entirely different construction and what got me to thinking about its origins.
Dave