I may be mistaken but wouldn't crews spend their nights at a local hotel or some other place like that? In a that case all you'd need is a place for a company vehicle to pick up the crew, make a loop and head off to the crew quarters (I've seen similar 'taxi' service at CSX's Rougemere yard).
Another possibility might be for the crew to overnight in 'their' caboose. Wasn't there an article where the railroad provided a coaxial cable drop so the crew could plug their tv into it while they stayed in their 'hotel on wheels'? I know back in the 60's some crews would personalize their caboose with ornamentation (favorite college colors, license plates, etc) to make 'their' caboose stand out in a string of them. I got that last bit of information from the C&O Steel Caboose book...they said the railroad probably didn't give official permission to customize their caboose, but it probably happened anyway (especially if the boss rooted for the same team!).
The only structure really 'needed' might be a shed to store consumable supplies for the caboose and loco, like water, cups, fusees, torpedoes, toilet paper, fuel for the stove, spare bulbs, etc. Bigger replacement parts might be stored at an engine terminal or repair facility.
If you're set on a building of some kind, a boxcar, ex-MOW, passenger/baggage or even an old caboose would be easy for the railroad to put on a flatcar and drop wherever it was needed. I would think any structure or shed would look just like other railroad buildings, but maybe add windows, A/C unit, smoke jack, tv antenna and telephone pole to carry communication and power lines.
Sounds like a fun project! I'm designing a yard too and have been looking at prototype photos for inspiration and reading as much about the subject as I can find. You might want to check your railroad's historical website for ideas. The COHS is free to search through the archives and there are plenty of books, pamphlets and drawings to buy too.
