All I can say on those super-large mobile cities is that they are likely a set of 9 linked structure components (5x6-6x6 in size) that collectively cover a ground area about the size of single mapsheet. They are track-based, and may appear in a number of strange configurations.
The three I have on file are known as Metro-Central (AutoBoP [Metroplex]), Tri-Central Command (DemoCon [Trypticon]), and Titanianopilis (Democon [Metrotitan]).
I never statted them, in order to maintain my own sanity, but I imagine the outer structures would generally feature weapon emplacements, while the central structure contains command centers and repair/supply facilities.
- Herb