I think of it as a machine shop...
Quite a long while ago now, I scratch-built a curved building to fill in one corner of the layout. I think of it as being a machine shop. No rail service, but the tracks run right past it. Located just across the tracks from the JSSX locomotive maintenance shed, this structure actually turned out better than I had thought it might. The tracks are probably a few feet too close to the building than might be prototypical, but I didn't think of that at the time, so I live with it.
The base of the building is cut from a piece of scrap plywood, and the walls are basically 1/8 " MDF with concrete block sheet that I've laminated onto it.
This view below through the back shows that I've braced the curved wall from the inside with scrap pieces of 1x2.
Taking a lesson or two from the well-known modeler Lance Mindheim, the large roll-up door is a photo I took of a door on a welding shop here in Sarnia. I framed around it on the structure with some narrow strips of Evergreen styrene.That trash dumpster is a free printable download from Lance Mindheim's website. A little tricky to fold and glue because the printout is little, but it turned out well.
The windows on the machine shop are from another photo that I took of a local building, which was actually a former spark plug factory (Presto-Lite Spark Plugs) built for the WW2 war effort. I lost that photo when my laptop crashed last year. The windows on the prototype structure have all been replaced with new modern ones. On my structure, I cut out the concrete block sheet to fit my photo's printout. I also framed around the windows with styrene. The pipe that runs along the top and the brackets it's attached to, along with the drain pipe provide a little more "relief" to the structure. The graffiti is a about dozen or so Microscale decals
And since you've read this far along, there was a link posted on Trainorders.com this week to a pretty nifty virtual tour of the Blissfield Model Railroad club layout in Blissfield, Michigan. Their layout appears to be triple-decked, and there's lots to see. Use your cursor/mouse to navigate around the layout, in much the same way as you would on Bing or Google Maps. You can also click on target points of interest for a better view and a written description. It's really pretty cool. Link to the Blissfield club's virtual tour is below...