I honestly rarely go on roofs when I am an archer, and when I do it is usually because the map is terrible and my team brought only two pikes and all the cav were stacked on the other team and everyone is splitting up.
I noticed that I have an easier time shooting other archers when they are on the roofs as compared to the ground. Last night, almost everytime I shot and killed an archer it was because they were in a cramped spot which made their weaving predictable (a narrow street or on top of a roof). I also notice that more often then not, roof camping gets me shot faster then staying on the ground. The main advantage in my eyes when I roof camp (besides the 96% immunity to cav, ignoring those that somehow fly their cav into the sky which always makes me chuckle) is that I don't have wanna-be bodyguard teammates weaving in front of me to tk...
I would not mind too much if the devs disabled ladders on battle for a couple of weeks just to test things out. It need not be permanent, just a small test, then put the ladders back in while they contemplate how it has changed things. While I am not totally comfortable with removing ladders, it does sound intriguing. Of course, you could argue that I am biased since I rarely roof camp and spend most of my time on the ground...