In addition to the excellent points that Greg made, Sketchup is pretty intuitive. I have used 6-7 3d modelling programs and used to teach Rhino and Maya (these are not what you need), but sketchup is by far the easiest to teach. Its integration with Google Earth makes it an ideal way to integrate on an urban scale. You can bring a map in as a pdf or a jpg if you don't want to go the Google Earth route. Just drag and drop.