I'm in the process of designing a big one (40+") to house steam and diesel engines. I have an Allegheny and Pennsy S-1 which accounts for the extreme length. I'm deciding whether to have the "kit" cut with a friend's CNC mill or having it laser cut. I'm not ready to pull the trigger yet, so I have time to decide. Originally, I was going to have custom windows laser cut, but now I'm resizing the openings to use stock windows from Rusty Stumps.
This version has the custom windows which will be bigger than the Rusty Stumps stock windows. The drawing was done in SketchUp laid over actual Google Earth Track images from a Louisville, KY rail yard.
SketchUp also gave me the ability to render and interior. The GP-40 was pulled from their 3D warehouse. Someone somewhere was nice enough to draw one. All I had to do was click on it and drop it in. In SU you draw at full scale so all the images in the warehouse are properly scaled for whatever you're working on.
The overhead gantry crane will have to be scratch built. Clearly, the long inspection pits will require some interesting solutions when using 3 rail track. Some fellows have strung some bare copper solid strand wire under tension to serve as the hot rail while making it very subtle. My 3.5" Ross #4 switch track spacing creates a very narrow space between tracks to have work platforms.
