I seem to have a problem with walls. Specifically I want to make an outdoor level with a structure that the player can enter. So I'm using forest_ground as the base tile, and castle_wall for the walls. Only that doesn't work - the walls block movement and show up on the map, but are invisible (see screenshot)

So the first question is: Am I doing something wrong here or does that just not work?
Second question: I proceeded to build the structure using the wall components (not the tiles) and started to have a shadow problem. While I figured out that i need to "double up" the walls so they block sunlight from the other side, I don't know what i can do about the ceiling

This screenshot was taken looking at the sun, you can see the walls throw a shadow while the ceiling doesn't. Any ideas on how to fix this?
And finally, an slightly unrelated third question: I wanted to create a "magical" structure that is bigger on the inside than the outside. I have implemented this using invisible teleporters. Since walking into this teleport triggers a visible effect, I have made a timer to wait until movement is complete (0.2 sec seems to do the trick). So you walk into the disabled teleporter, trigger a floor trigger, which starts the timer, and after movement is done, the teleporter activates and sends you to an identically contructed level somewhere else. Apart from this being visible on the map, do you have any ideas how to implement this in another/better/more elegant way?
Thanks already in advance,
Sharkeem