Great start,
You could try assigning an Arch & Design material to your ledge, with Ambient Occlusion turned on, that might help alittle. And as Jelmer said, once your FG settings get better, so will all those small detailed areas (and render time)
I like the floor, it has solid potential. But you might want to play with the reflectivnes of the ceiling, I think its slightly to reflective.