Need Westside Bakery that does Theme Cakes
I have seen many bakeries' catalogs that include lots of theme cakes. Victor Benes does this, but at a premium. Angel Maid on Centinela in Mar Vista does this as well. They're not cheap - I would consider them mid-range - but I would strongly assume that if you brought in some kind of image and talked with them, gave the approx. dimensions or had them suggest some, you'd walk out satisfied. In general, Angel Maid has very light cakes, both in texture and flavor. I don't know if this suits your friends.
Angel Maid Bakery
4538 S. Centinela Ave
LA, CA 90066
Another place that I've taken a recent liking to is Buttercake, a tiny bakery on Pico in West LA/Rancho Park (thank you, Pei). For shear quality of their cakes (they're known for their cupcakes as well), they are very good. I don't know if they do theme cakes, but if I were to have one of their creations in a theme cake, this would make me delirious.
10595 W. Pico blvd
LA, CA 90064
Hansen's Cakes on Fairfax has had a long-standing reputation for theme cakes as well. I personally have never had their cakes but they have been around for quite a while.
1072 Fairfax Ave
LA, CA 90019
I'm far from an expert to consult on this, but considering that you're talking about a cake with potentially several layers on the scale of a miniature multi-story building, there might be structural considerations to ponder over - both in creating as well as transporting this cake. Most cakes on this scale are tiered, where the individual layer cakes are supported by piers - I would guess this particular one wouldn't. Some things to think about? Good luck!