This sounds like an amazing project. There are so many directions in which you can take this paper. So, let me give you a few suggestions to whet your appetite.
First, if you need some social theory, I suggest Peter Berger's Social Construction of Reality. In this book, he talks about how all societies are constructed. This is why one city or place differs from another. After a society is established, the construction of reality has a commonsense notion of what is self-evident. To capitulate to a social norm is to be institutionalized. To go against it is to incur social alienation. Just this framework alone can give you enough to write ten papers.
Second, as for topics of interest, you can write about any subculture in cities - immigrant populations, religious sects, or something like private school—the sky is the limit. For example, Nels Anderson, a sociologist of a generation ago, wrote a study on hobos (1923).
A topic that fascinates me is power in cities by looking at wealth. Bourdieu's theories on social capital and symbolic capital are very insightful. However, a warning to the fainthearted - he is very difficult to read.
Another possible topic is the continued growth of cities. There are three cities now that have over 20 million people - Shanghai, Beijing, and Karachi. Delhi and Istanbul are not far behind.
Another topic to whet your appetite is the sociology of consumerism in cities. Here are some final ideas: sociology of youth culture in cities, technology, terrorism, gender, and the like.