Call 360 Design Group, They are a small architectural firm that specializes in roof decks, rear decks, and building voilations. They will come out to your property and give you free advice. They are a gem when it comes to decks. Quit talking to contractors and talk to design professionals. They will provide you with permit / construction drawings that meet the city requirements and even expedite your permit.
These guys are top notch! Not only did they help me, but many other people I know.
Ask for Bob or Frank, they were really extremely helpful. I cannot express how good this firm is.
Their office number is 312-842-2225 or email them at flevato@360dg.net or link@360dg.net.

lakeside Exteriors will build roof top decks, they have architects on staff call Alan Nitzkin 224-723-6636

Here is some information on roof deck requirements. Hope this helps...

Roof Decks on Primary Buildings

Building a roof deck requires a Building Permit. A roof deck must be designed to meet the structural and architectural requirements of the Chicago Building Code and plans are required. These plans must be prepared by a Licensed in Illinois Architect or Structural Engineer.

http://egov.cityofchicago.org/city/webportal/portalContentIt…

Before you do anything, are there two separate stairs to the roof or ladders? If you are going to build a roof deck that is legal you need to have two exits. Keep in mind that if a fire were to start on the roof, the city code requires a second way of exiting the roof deck. This is the reason many new construction builders will not provide a roof top deck before the unit closes. They are concerned about city inspectors.

Although you may see many roof decks in the city that do not fulfill this requirement, bottom line, they are not built to code.

Cintia,

I would start by talking to an Architect. They're the ones responsible for certifying any drawings which the city will use to issue permits. As previously stated, you must have 2 exits and meet strict weight limits and have a building structure that can support a roof deck .
Often, if the top floor unit owns the Roof Rights, they can build a deck. Doing so would likely make any current roof warranty void in the event of damage caused by the deck to the roof membrane. If the association is responsible for the roof then it would be the unit owners (two in your situation) that would vote on such an addition based on the Condominium documents and pay according to % of ownership.

If it can increase the marketability of your home by offering stunning views it may be worth doing. But if you can't do it right and comply with city code, you may undertake expensive work that ultimately could be shut down during construction or be requested by the city to be removed after it's already built.

Best of Luck, Ken.

Try the building department for the City of Chicago.

I would first find an architect. Anyone who does work in the City will be familiar with the City's structural (100Pounds/SquareFoot) and exiting (2 exits?) requirements. These are two big issues that are seen on all new roof decks. These are also potentially a deal breaker due to the expense of structurally reinforcing a roof to hold the weight and extending 2 stairs. To find a good architect just ask around in various places, Real Estate Offices, Renovation Contractors, and neighbors also doing work. They should be able to give you an idea of what will be required (costs, permits, time) without a fee.

Your first call should be to your alderman. The alderman will be consulted before any rooftop deck building permit will be issued, so start there. Assuming it's approved, you'll need an architect to design it and a reputable contractor to build it. I agree with Marek, that Zee's Group seems to do good work.

Sure. Try http://www.zeesgroup.com They are reputable company and will help you out with any questions you may have.
Mark