Block building on cieling

I have a room where players fight, the players can place builds inside the room as this is a boxfight room.

It is also possible for players to place builds on top of the roof of the room from within the enclosed room, which is problematic is several ways - the roof covers the entire room.

Im looking for a way to block the ability to build, on top of the roof from inside the room.
I’ve tried some ‘creative’ ways like placing a barrier on the roof, which did blocked the ability to place builds but added noticeable lag/delay to building within the room.

Looking for the proper way to disable placing builds on the roof, from within the room.

Your other post where you set the prop to attach floor… I would have thought that would’ve worked for this