That looks better, but it still suffers from a lack of depth. By placing everything so close to the edges, I get the impression that there's nothing behind the walls.
Detailing ceilings and "out-of-reach" areas are one of my favourite aspects of mapping, because there's so little detailing needed to achieve so much.
I only have access to paint and a touchpad atm, so bear with me here. :P
[lvlshot]http://i.imgur.com/c1ilODV.jpg[/lvlshot]
My picture shows a terrible representation of what I mean. The red colored and the purple colored boxes are structures, and the black lines are wires. These are just examples of what could be going on, but the important part is that both red structures base are placed behind the edge of the current highpoint of your wall, and the purple structure is even further back. This means that at certain parts of the map, a player might not even see the purple structure, but as he moves higher up, he'll see more and more of it. The detailing up there doesn't have to be complicated at all. The windows you've placed would also change to reflect this, maybe adding LOS to one of the walls of the structures.
Hope this helps.
