Making a city cake for a 30 year old "boy" -have some basic ideas of what i want to do but any suggestions of what would be nice to put on it or the best way to make.my buildings welcome

Just to clarify, the train will be running around the outside of the cake not through it.

Sounds wonderful and a really fun project! Do you want it to be a realistic city or more a animation type? You could base some of the buildings on actual buildings in yours/his town or landmarks from a nearby city centre and terraced houses should be easier to fill in some of the streets between more elaborate buildings. You can add as much detail as you want/time allows. How big is is going to be? Oh such a fun project!

One other thing, do you want actual cake or could you use gingerbread? I got this book http://www.amazon.com/dp/0307406784/?tag=cakecentral-20 as a present and it has AMAZING houses in it, I'm sure you could make them much smaller or just use it for inspiration.