Hebelup,
I think the modeling is clean but there are a few issues.
The curtains are all the same and the repetition is obvious. That is one thing that will stand out right away. Try tweaking them to make them all a bit different.
The scene needs far more vegetation so the building does not look to just be dropped on a concrete pad.
Try to show a view that shows the entry to the building. It looks odd that there are no ways of entry from this angle.
The background does not blend to the scene.
Some cars and people are needed to give life to the image.
As said before the building is too clean.
The yellow stripes are too bright and draw your eye away from the building.
The composition/view is too close to the building and does not show how the building affects the surroundings.
Your on your way but the image still needs some work.
Scott