Great Job.
Personally...
You can modify the roof... making it a little more large than the walls.
Also can add some decals like ivy on the walls or a pipe, or something to do a more dinamic apparience. A ventilation grid at ground level on the garage lateral wall.
You can also a window frame or something similar...
You can add what you want to make it more... realistic.
wel looks good, could do with more detail, but the main thing that stood out is the tieling on the room, on the virtical part of it, it just joins into the wall, and in reality those tiles would fall, you would have to redo the vertical part of the roof. the rerst looks good.