There's something I'd like to know; do you do your sky so grainy on purpose, as an artistic idea, or is your intention to make it a smooth, realistic image? In the latter case, I'd work on the quality (RayTrace Atmo, or higher samples). The same about the glass panes and iron bars; there seems to be some sort of displacement in it. The glass's transparency may benefit from the addition of a reflective shader after the glass shader, and the glass shader should not have any waves (or it'll break up the glass, which is sometimes a nice effect, though).
