If the object you are using is "scenery" the AI grid will not update. You can see this on the side bar.
To change that you need to change some of the settings on the side bar like give it stats or make it movable.
But the bigger problem is that many objects in the game do not have that purple dynamic AI painting that you see from stuff like tables and chairs.
My suggestion would be to look through the root templates and place objects till you find one that has the purple AI coloring.
I'd say look at PUZ_DOOR_DungeonPrison_A
You can stop it from being a door by removing the "on use action" if it has one. Then you can use the scale to make it bigger if you need.
Also don't forget that when you change some items on the sidebar, for it to take effect you need to do a cntl+r.
Last edited by SniperHF; 27/11/15 11:16 PM.