I don't have something like that, but I am also a bit of a fan. However, there are a few "conditions" that would have to be met for me to build a roof terrace. For one, there would be no or too little space in the garden or on the ground. On the other hand, if the terrace on the ground could be seen by everyone (personally, I don't like sitting on display). The location on the ground would be bad. The terrace on the ground would, for some reason, not become particularly inviting and cozy.
The roof terrace would then basically have to be connected to the kitchen for me. You don’t want to carry everything from the ground floor (where the kitchen is usually located) all the way up to the roof. Just think about barbecuing with family or friends. A bathroom/WC on the floor, which probably won't be a problem. And it would be important to me that the roof terrace is accessible without having to go through a bedroom, for example. This is not relevant for residents, but I wouldn’t want to have to always lead friends, family, and distant acquaintances through my bedroom. Then the roof terrace should have something to offer, a nice view over the village/town, a secluded place, full evening sun, etc.
I think usually people will build the terrace on the ground. That makes the most sense and is more cost-effective. Usually, garden design or the layout allows the terrace to become a cozy and relaxing place. Only if that is not feasible would I, even though I love such "quirks," consider a roof terrace. A sunny spot to relax for an hour or two can also be achieved with a balcony.