Start with a real estate agent. Ask whether or not dropping a couple of hundred thousand on your existing home would be recouped or if you're planning something "above the neighborhood" or whether or not it'd be better to sell and take those thousands and put towards a home that is larger and more suited to your lifestyle from the beginning.

Thanks. I appreciate your response. My house is "below the neighborhood", so I'd be building "up". Now ... my house is fine. It's antique and small. Most of the others in the neighborhood are newer (1980's to 2000) and much larger. Of course, it still may be better to sell and buy, but I just wanted to make sure it's clear that most homes in the neighborhood are worth more $$ now.

The agent can tell you if it would be worth doing, but the codes office will tell you if it is possible and how much room(and where) there is for an addition. Property setbacks and utility/city right of ways limit expansion in many cases.

The current foundation may not be sufficient for a second story and the surrounding ground may limit the types of new foundations possible. An engineer should have that information.

And finally, an architect and their blueprints will often be necessary for the permits. Some contracting companies may have all or some of those folks.