After research and talking to a friend, i've found out my model isn't a Bachmann GP38 but a Aristocraft GE u25B in scale 1/29....this means the era i have to make is between 1965 and 1975
Well. Sort of.
The Union Pacific U25B's were built in 1961 and 1962. They were retired in 1972. During most of that time, they were likely in mainline service. So seeing just one at a small enginehouse would be very unusual.
Some of them ended up on the OC&E, a small railroad that went east out of Klamath Falls, Oregon. Roughly, in 1976. And they, again roughly, lasted until 1991. IF you wanted to repaint and reletter yours, they were done in this attractive color:
Should you NOT wish to do a repaint, you could argue that they just arrived and have to be put to work right away.
Anyway, here's a picture of an OC&E enginehouse:
Note the main doors, and above, the auxiliary doors for the craneway. You can see the building has some length.
Being black and white, this building might have been gone by the time the U25B's arrived. Or might not. But you can see a typical enginehouse on a railroad where "your" U25B ended up. As OC&E 7605. For awhile.
You can learn more about the OC&E from the book by Jeff Moore: "Eastern Oregon Shortline Railroads".
Weyerhauser (a big lumber company) also got some, and they were also painted nicely. There's a lot of material about Weyerhauser out there to learn from.
You can learn more about Union Pacific U25B's at the website Utah Rails.
Engine houses were not houses for engines. At least, in later days with diesels. They were places where work was done on engines. As such, there was a sheltered area to work on the engine. And a shop with benches and tools. There was also an office. And there was a storeroom for parts and materials. Only small quantities of flammables would be inside--large quantities would be stored a safe distance away. Oh, yeah. A bathroom. And maybe a locker area.
If you are more in a freelance kind of mind, a few comments:
Enginehouse design was based on four main things: era, location, number of engines, and amount of money to spend.
The first is, indeed, pretty much set for a U25B. But I would argue that, in this case, it is from about 1975 to the present.
Location affects building style. In a warm dry area, you almost don't need walls. And, since you generally WILL have (some) walls anyway (security concerns and all), there will likely be a door at EACH end of the building, to catch a breeze. Also, on the west coast, masonry would be rare (earthquakes). Generally, though, in the post 1975 era, these buildings will be metal sheathing over a steel frame. Second might come concrete block, or maybe a "tip-up". Wood sheathing and framing falls out of favor for fire safety reasons. Even if it is attractive and nostalgic.
Number of engines. Kind of self-explanatory. The more engines, the more stalls.
And then there's money. The chief mechanic would DEARLY love to have everything that enters his mind. Preferably two of them. The financial officer might disagree. But if the mechanic makes his case and the money's there, the thing gets bought.
So, to the details:
An engine is always nominally 10 feet wide. Add two feet on either side for person passage, and you get a door width minimum of 14'. 16' might be the max. Height of door would be enough to clear the engine. Diesels are all about the same height. About 15 1/2 feet high. So a minimum clearance above rail top might be 16 1/2 feet. And maybe 18' for the max needed clearance. That's the door dimensions.
The building has to be long enough for the locomotive(s). And the railroad doesn't want to find out when they buy another new locomotive that there's a problem. So I would go with a locomotive length over couplers of 66'. Then add 4' on either end for person clearance. And add 2' for wall thickness. And get a recommended length of 76'. Minimum. The mechanic might well yearn for another 12' or so, so that he can jack up a locomotive and roll a truck out for work. Inside height at the locomotive should be at least 24', so that workers can stand straight up on top of the loco. If there is a craneway, additional height will be needed--allow for the height of a typical lifted part, the crane and craneway. You DON'T need the height of a real locomotive shop, where they might lift and transfer an entire locomotive. I'm totally sorta guessing, but I'd add another 12' for that device. The height of the rest of the building will proceed from this dimension. The width inside will be based on a 10' wide locomotive, about 4' of clearance (minimum) on each side, plus the width of the necessary shop.
There has to be at least one "major" door. Frequently, the track goes out the back aways through another major door. The chief mechanic will be happier. A second parallel inside track (and door(s)) can be very useful--ask the chief mechanic. The shop area has to be big enough to work in and to hold the tools, large and small. It tends to be on one side of the building because you don't want to have to "crawl over" the engine every time you need to go to another task. Storeroom and office dimensions can also be developed from imagination/real life.
The inside of the building would likely be paved, excepting the office and bathroom. A pit between the rails could certainly be useful, but I don't know how often they were used in a building like this. The office would likely be heated.
Car repair work could also be done in this building. Especially on a cold rainy day.
Windows (those big multiple ones) seem to happen less often with later buildings.
A building like this is perfect for an interior. And lighting.