This seems like a great idea for the students. They will enjoy the idea of recreating their local area. The idea of rotating the groups might cause some dispute or demotivation with students but i would be keen to find out if it worked for you. I can foresee some student half way through building a house they are very proud of and then being moved to another group, thus becoming disappointed. I have found that when the students are kept in the same groups they become very proud of their work over time and even compete against other groups. I have also found that having prices for best group-work, best building, best overall town etc really motivates the students during this project. It would be interesting to see the students look at the new rail line plans and to include these in their builds. Well done.