Update

I'm working on the map of the city at the moment. The book I talked about earlier has been a big help - I've found a lot of tips in it which has made the process easier, I've learned how to import screenshots from Google Earth into SketchUp as guidelines and it's also helped me to learn how to export the SketchUp map to Flash. This seems to be quite a complicated process and I'm planning on doing some more research into this very soon and try to export some more simple models into Flash to see how it works.

One problem I've been having with SketchUp is that it has been very slow already and this will probably get worse as I add more detail. I'm thinking of splitting the model into individual files - one file per building and combining them at the end.