Basically, have a skeletal core that can hold a pose that disconnects, with shaped Styrofoam inserts you get from computer packaging and the like for the general details and shapes of the city and body. Smaller details can be whatever you like, but preferably simple, replaceable pieces. Transformations should be primarily horizontal, since you're using Styrofoam primarily. Once built, it would allow for a light, maneuverable figure that could tower over your other TF's properly. There is, of course, issues of styrofoam getting damaged, but just have a Godzilla toy handy that you can blame. Is there anything like this already out there? Does anyone have any ideas on how to keep the lightness but reinforce the material used?