Strange, I was playing a GBA game where there's a Mansion area and in it there are a few short points where you can access the exterior sections of it in order to access other portions of the interior. In the English version's Sound Test the name for the BGM used there is "Roof," however, when I inspected the original Japanese version's title it was "屋上." Most of these sections are just small walkways, but I'm uncertain if they'd be considered a rooftop or not, maybe they'd count as a "terrace" since those seem to fall under the description of a rooftop. Though there is one part where you are undeniably on a part of the roof itself, so I imagine that the original title must be referring to the walkways, assuming that they actually count as rooftops.
I checked 屋上 in a corpus, and confirmed that 屋上 referred to "flat rooftop" in all the first 100 search results. A dictionary indeed has the definition 屋根の上 "on/above the roof" for 屋上, but the example where 屋上 means "on usual roof(s)" is just only one あの家々の屋上に引き散らしたアンテナに対しても同情しにくい心持ちになる。 among 24 examples in the dictionary, which is quoted from an essay published nearly 100 years ago. Whether 屋上 actually refers to "on/above the roof" or "flat rooftop" in the game, this is the usage of 屋上 in real life.