I've seen the trailer (and that building thing), and all I can say is :lol:
It's possible (as I see it) to do it in two ways:
#1: You need to have someone at the top breaking the rope for you.
(the stuntwoman did probably have that, but Milla was alone on the roof)
#2: you could have some kind of automatic breaking device at the top, that slowed down your decent.
But stoping/slowing down before you hit the ground would have been VERY hard to do..
Unless you have measured the exact lenght of rope so you would stop just before you reached the ground.
(but she didn't do that in the movie trailer)
So the stunt is possible to perform, but not the way it was supposed to look like in the movie (without help).
In order to do that you need throw out the rope first, and use on of your hands to break on your way down.
That's possible, and very fun..