We have real and recent experience with a rooftop deck. Two matters need to be considered: noise and privacy. Noise travels freely from such a deck, as anyone knows with roofing work nearby. Further, the timing of such noise tends to be when people are at home (ie. evenings and weekends). Our neighbour has a part-enclosed rooftop deck and the family has parties which sometimes continue into the night. From our house it seems as though they in the next room.
Lastly, a rooftop deck means rooftop views, so if you value the privacy of your garden then this can make you unhappy.
These rooftop decks may seem a nice idea for one owner but in practice can make several neighbouring owners upset. Not a good idea in such a dense suburb.