Its off to a really nice start. Id just suggest watching your scale as you bring more and more things into it; keep your reference character handy as you import textures and objects. An elevator hallway between the blue columns would probably help that area a great deal, and instead of the short, ramp-like stairway you have coming from the mezzanine to the second floor, maybe more of a sweeping ramp that comes up from just off the center of the mezz level to the second floor: itd add a little more balance and movement to the area. Instead of railings, how about glass walls facing the atrium level? Sure itd blow the render time up, but railings might wreck the elegance of what you have at the moment. Finally, for the office doors et al, make them part of the texture wrap for the walls instead of building them in as objects. Itll ease the model size and you really wont lose that much in detail.