Roofs are common practice on that map now.
People know that you can be there - but you still have advantage - that roof is pretty big, and it's hard to be hit just from anywhere - so you have possitional advantage and of course advantage against those who don't know that you may be there.
There're planty of places like that on different maps.
I suggest us to go to Deathmatch server (which is not being used during the night in Europe) and test different places where we can get advantages from kneeling.
Among those places can be even simple boxes that are impossible to jump too... Let's say you playing for T at inferno - you can plant bomb on the top of the boxes - it's guarantee win if only one CT left, doesn't matter how good he is. I believe same thing can be done at dust2, arena, aztec, aztec3, etc