Way to design a rooftop deck cut out of a gable, hip, or gambrel roof?

[cbucks]

In an area I am working in they define a half story as a  gable, hip, or gambrel roof where two exterior opposite wall plates are not more than three feet above the floor. Client wants a rooftop deck. I've seen a couple homes where it appears they cut out to do this but wanted to get some ideas and opinions on this? My fear is it may be a big problem over time.