I guess a general piece of advice I could offer is to give your building depth - it can still be a rectangle but have some parts and such sticking outward and sticking inward among with other things to toss in some depth. In terms of the roof, if you're going for a flat roof kind of look, to make it seem less, well, flat, add an edging around the border and such; If not a flat roof, try out a gable roof.
After loading it up, yeah, the difference in roof height is a bit odd, but I think this is caused by the white stripe cutting across the left side, as on the left side there isn't actually a second floor, there are stairs that lead to the porch-like area. Also, the building itself could use a proper building - you kind of just kept it as a hole - so try to like, patch it up and toss a door in or something. It's kind of difficult to really pinpoint what's wrong and what's right with your build since I stink at relaying an opinion, but I would definitely recommend taking a gander at like cities in real life, in LEGO or in Blockland and seeing how they're structured and what makes them interesting. I would love to see further improvements in the future though!
