Okay this is what I like to do cause the idea is that the roof tops are not perfect snippers nests. any time you are at an edge you can shoot what's in front of you per normal. but let's say you are one square back from the edge. then you can not shoot at the square on the opposite edge of the building. this gives someone chance to get the guy on the roof. So you can circle around the building using the building tween you and the snipper as cover. so the rule continues if you are three space tween your fige and the edge you can't it anything in the first three on the other side he can't hit.

and I heard someone else do this and I like it too, anyone hit with three clicks of knock back into a wall that is only two spaces away, the figure breaks through the wall. course this is only on indoor maps