Okay so I thought I'd do a thing where I show you how I did some of the art work.
These are the backgrounds. I modelled them all in 3d. From this render you can see the basic structure of the city.Setting up the scene and camera to the right perspective etc (takes a while to decide which render is the best afterwards).

Render.

Dragged file into flash... draw the lines over the top of the picture. You probs cant see it properly, transparent png..

Colour it in. Gradient that shit. Yeah, it's missing windows and stuff. I got tired of drawing them all in and decided against it. You can all just pretend they're there. Cmon use your imagination. :)