How long does it take you to model a building in SketchUp? Ok, how about a city block of buildings? How about two dozen city blocks, including all streets, sidewalks, buildings, water and trees? If your answer is "More than 6 mouse clicks," then you NEED to check out this episode of Extension Inspection!
Check out PlaceMaker on Extension Warehouse: http://extensions.sketchup.com/en/content/placemaker