Hello Irene, I am also a licensed contractor here in Denver and built a few additions. There is a lot of good information below. The walk-up desk can be a great resource. A knowledgeable contractor will be your greatest asset. I would contact a builder that has done some additions in the City. Have them look at the property before you close. Zoning could be a potential road block. My argument to them would revolve around the fact that the neighbors have similar additions. They will have a hard time saying no if that is the case. I have actually found the Denver Building department easy to work with.