I recommend using 2 by 2 foot sections instead of 1. They get crowded way to quickly on 1 foot square.
8" roads sections are fine. However, a main boulevard that is larger can come in handy.
Two general tips to city terrain. Be careful to avoid a simple grid pattern. This leads to real predicatable killzones and firing fields. Try roads that are geometric as much as possible, or have artificial roadblocks.
Second, the exterior color of buildings should not be the same as the interior. Add some blasted off wallpaper, or scorched paint to interior wall sections. This will add color to a drab board and add to the effectiveness of the terrain.
Lastly, I recommedn you look at this:
http://us.games-workshop.com/games/40k/cityfight/terrain/cardboardcity/Default.htm
Good luck and keep us updated.