The easy way to do this sort of thing, I think, is to use GCM's Foam Board Buildings.
I knew about these foam board models via TMP News for some time, but until this week I had not given them much thought, because they are very base components with no detail. I had the forest for the trees mentality about doing large buildings to make up a full tabletop.
"Hey Joe if you want Green Buildings you should use base shapes rather than detailed models...dummy."
Yeah. Of course, the details come from the lovely greenery and odd little bits like rusted girders and massed vines clinging and crawling up the structures!
Funny that the simplest and most efficient answers can elude you for a time...
I am going to order a few of these to fill in my city, and do some Hero Models to pretty-up the overall look of The Dead City Board.