A word about AI meshes:
AI meshes are the pathfinding meshes. It walks over these AI meshes to get at an enemy. AI Barriers are used to not make AI's fall of ladders, while players can jump off than, unlike when placing normal barriers.
Best way to make AI meshes on walls and through buildings is by going to Edge mode and extrude them.
If an AI mesh goes through a building, the AI will think they can pass through that building to get at an enemy, so don't do that. If an enemy is on a place without AI meshes, the AI will go to the AI mesh closest to him, and tries to reach him from there. If the bot gets off the AI grid, he will try to get to the closest AI mesh, sometimes being at the other side of the wall, thus bots gets stuck under ladders. Also add AI meshes under ladders that lead them back to the ladder.