I think it's important to decide how much you actually want to depict. In my case I have a city (Riverhewn) that is the capital of a large kingdom the city is home to about 150,000 which as fantasy cities goes is pretty large. I went with a "city block" technique that emulates "blocks" of buildings with the negative space in between being streets. It's a process to be sure but it is much quicker than trying to draw each building by hand.. Good luck I look forward to seeing what you come up with ..