I am planning to add a single story room to my house off the family room. I would like to have a usable deck over the roof of the addition to be used by the upstairs rooms. I am guessing that I build a low slope roof (1/4 inch per ft) with some type of membrane roofing system, but don't know how I would attach the deck on top of it. I can't find any design/construction systems or details to tell me how to construct this. Any help would be appreciated.

Rooftop decks are just a plain bad idea, in my opinion.

First, you will need to have you roof and rafter system engineered and to carry the excess loads of the deck and lots of people on ot.

Second, building a deck over a roof never takes into account just how you will replace the roof in 20 years without deconstructing the deck to do it.

Plan another option for a deck and allow the roof to do what roofs are supposed to do.