This article may help you in your roof deck situation...
You have all the facts from Jeff if you are thinking of doing a roof deck in a single family, however, if you live in a 3 flat, 6 flat or 8 flat, I strongly suggest you do additional research and find out the rules/regulations from your condo board as well as the original property report. Please read this information carefully to discover what liability you could encounter should you decide to build a deck. I strongly advise you to also check with an attorney.
i'd probably also take a peak at muncipal code, sections sections 13-124-310, 13-124-320 and 13-124-330 (google chicago municipal ordinance to get the complete verbage).
best of luck, and don't forget your trulia friends at that first bar-b-que!