I make maps and I put barriers on roofs I don't want to give access. I also leave 1-2 roofs open for archers. But those roofs always have a permanent access point. Because of the way people will exploit anything, I am also forced to put barriers around the entire map as well as a ceiling to prevent ladders to heaven.
If ladders are not removed, the people in charge of putting maps on servers should reject all maps without these precautions and retro-fit old maps to meet this criteria. I'd even volunteer to do that shit because I hate ladder campers so much. If you see a problem on one of my maps, please let me know so I can patch it up. Heavy laggy forest map, bloody/smokey/fire battlefield, and two keeps over a river with rope bridges connecting are mine.