Rooftop Bars/Restaurants

My dad's having a meeting for his company in Chicago and he decided to fly my mom, brother and myself there because it's over my spring break. I am actually turning 21 while I'm there, so I am looking for somewhere sweet to get completely hammered at. In Boston, there is a restaurant at the top of our second tallest skyscraper, The Prudential Center, called 'The Top of the Hub'. I assume that we're not the only city to have a top floor restaurant, and was wondering if there were any cool restaurants in Chicago that were on the top of skyscrapers, and if so, what were some cool ones? Thanks for any feedback you guys can give me.>