Well, you know have they have flat roofs in various parts of the world. In Ancient Egypt (I don't know about Modern Egypt), for instance, where they would often sleep on the roof because it was cooler. Now, why anyone would be sunbathing if they were in that part of the world, I don't know. :-)
Well, you know have they have flat roofs in various parts of the world.
Usually not where there's likely to be lots of snow (like the other places you mentioned) :)
Actually even in snowy places apartment/office buildings have flat roofs - I can only assume it's because the collective heat coming from the whole thing melts it so you don't have that "hundreds of pounds of snow threatening to collapse your roof" problem.
In general American, "getting a tan" would describe a change of color resulting from multiple episodes of sunbathing / tanning or working / playing outdoors over an extended time. Using that expression for a single session would be a bit of a stretch UNLESS you were referring to an overall program of tanning in which that single session was only a small part. "Tim lies out on the roof every day during lunch hour because he's trying to get a tan."