Somewher I've got GW's old floor tile set for Judge Dredd/Rogue Trader... and it came with a booklet that had random generation tables for huge urban hab blocks. Maybe too futuristic but that's the sort of thing I might start with... and have a bunch of standardized apartment/shop plans that I can pull from. Beyond that, just capturing the atmosphere... smells and sound and NPCs... vs. trying to map it out with any precision.