Moll, you're definitely right! I live in a flat in London and we have a roof terrace and we're moving (fingers crossed) soon.
The roof terrace conforms to all building regs, ie there are iron railings all around, with narrow spacings and no gaps underneath, however ds is pretty much in to everything (he's 22 months) and although he's never had an incident, I'd never leave him up there on his own (certainly not for more than a few seconds). He peers through the railings which I'm fine with, but when he's indoors he's always moving chairs around so he can stand on them and look out the window so I'm terrified he'll do the same on the roof terrace.
Actually I'm quite nervous about him standing at windows 2 floors up anyway, I always remember Eric Clapton's poor little boy falling out of a flat window and dying. We now have window locks so we can have the sash windows open only a tiny bit, like an inch, so ds is safe.
For us though, the need to move was much more of a space issue. I know boys are sometimes more boisterous than girls, and ours certainly fits in that category, but all toddlers need room to run, and you'd have to have a pretty massive roof terrace to give a toddler the room to run around, and if you can afford that, you may as well go for a house.
Tell your dh about the house we're buying. It has massive bifold doors that open up the back of the kitchen/diner completely, so we fully intend to sit there on sunday mornings nursing a pot of tea and the papers while ds charges around the garden with a football, instead of hauling ourselves off to the park at some unGodly hour! Now how's that for not compromising your life for your dcs?
Try selling him that instead. Good luck!