Walther's Red Wing Mill

[2-8-2]

I'm using the Walther's Red Wing Mill (N scale) as the basis for a GERN facility on my new layout. I'm having trouble deciding what material this building would be constructed out of, had there been a prototype. My gut tells me poured concrete walls, but I'm not entirely sure. Most images I've seen of the structure show it in either a white or primer grey color, which is what I elected to paint it...but it's just not sitting right with me. Any opinions on this?

On top of that, I don't recall weathering a structure like this before. Most of my previous experience has been with brick or stone buildings, so I'm not sure how to go about applying a convincing layer of weathering on it. Suggestions?