i've got the exact same dilemma, wanting to do minor rooms within a bigger "play-area" with proper doors between them to section things up..

Hey, you can add walls inside rooms by adding for instance a shelf and then scaling it to make it thin. Then you add a logic element - obstacle, that makes it impasable. You can use anything to make a wall. https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2632496932

Now you can add pillars to this wall to make it more interesting etc.

Thanks for the comments guys. The work around I found was placing a Wall piece, then going into the Logic area and placing a obstacle that goes around the wall piece. it takes some work to get them to work when the wall piece is butted up against a door frame, but I seem to get it to work pretty well.