Well, now that the cat is out of the bag I might just as well admit where I love to camp (after Bridge falls but before Alamo is capped, mind you). EDIT: OK, this is not on the roof of any building, but anyway...
On the west side of the river, on the topside, go south to the tall building and to the very edge of the river (do not go down the stairs, stay on top), and if you're really careful, you can move south along the ledge (the arrow). Eventually, you can enter the circled building and can camp there and shoot through the windows. Even more devious minds can go prone on windowsills for increased accuracy. If you park a SL in there, a good squad is VERY difficult to force out of there (unless you know what is going on and simply park Tigger on the bridge and rotate the turret and hope that no bazooka hits your turret rear meanwhile and that the SL is not in a blind spot where HE won't get him).
I would argue that this is more fair than camping on the waterfront piers on the west side of the river after Bridge has fallen (which in theory is forbidden on 762 but blatantly violated and only seems to be enforced when I do it), as it's not in the flag zone (and does not even have LOS to the zone), and you use it to shoot Germans who are advancing between flags (and should be fair game), not spawning in uncap.
