Great work.

Not much to criticise except from your unusual use of shadows. Before adding in darker patches to your flooring you have to decide on where the light source is and take into account of the height of any of the level's objects/furniture/walls. Your third level is the best example of this. There are also a few minor problems, but I doubt having me highlight them will help.

I'll message David K to have a look through your work and spot for any problems, it would most probably help.