Storage units behind my house?

[Will Walker]

I'm curious what kinds of limitations I might come across building storage units behind my house hack. I see all kinds of spaces being rented out on Neighbor.com for example, why couldn't you build a few out-buildings/storage units out back? Is it as simple as contacting my municipality and getting the proper permitting. "I want to build a 3 car garage behind my house" kind of deal shouldn't be too complicated, but what else am I missing? This seems like low hanging fruit. Is anyone else doing this?

Thanks in advance!