Re-zoning a single family with the city

[Dagan Flowers]

I am looking in several locations in multiple states of lots as well as run down single family homes that meet my location criteria. However to maximize the scale of my business I want to re-zone these locations so I can doze the single families and build new duplexes. What kind of obstacles will I run into with local city governments trying to accomplish this. 

All my locations are in college towns.