Yep, looks good, needs something, and I know what! Slopes. Replace a few of those 1x2x5 bricks with slopes to give it a buttressed look.
Hmmm? Ok, I'll find a sample pic.
Blurry pic, but it isn't mine.
See the slopes coming out of the wall on either side of the doorway? Those look good when evenly spaced on an otherwise empty wall, like one of them, then 4 studs of flat, then another one of them, then a window, then another one, then more flat, etc. Alternately, you could do as this example shows and add some pipes or other metalwork coming out of the wall in places.
Lots of ways to fill empty spaces on roofs as well: antennae, boxy equipment representing cooling or power generators, pipes, junk, just about anything.
Keep up the good work and be sure to update us if you do more!