Here are links to help with the your urban planning.
Can't have a city without craters and rubble...
Now if I could only find those tips on vehicles...
http://uk.games-workshop.com/spacemarines/crater/1/ http://uk.games-workshop.com/cityfight/rubble/1/
In one of the White dwarfs there's an article on modelling damage to vehicles but I can't seem to fine that issue right now.