Ohh ok so you’re talking about two separate things:
- Custom mesh walls(etc) that the players can attach their player-built structures to, in game.
- Custom walls that replace the mesh the players place, in game.
Right?
Ya both of those sound great! I hope we get some answers, cause I have no idea 
I’m not using player building in my game so I didn’t even think about the possibility of players attaching their structures to my custom meshes.