The Red Mountain Depot model thats in the Silverton Mining museum was researched by Mr. Larry Brewer, an architect and engineer. There are no known "Plans per-se" but from numerous photos and such, you can pretty well figure out the interior wall and chimneys and such.. Door types, and locations, windows size and type and location give a pretty good idea of interior structures and why they would put a door or window where it is. Knowing that a typical door heights gives a good reference for size, and the same for windows of the era, allows one to pretty well extrapolate dimensions.
The model is shown with the roof open so as to see the interior.