https://www.nexusmods.com/fallout4/mods/108122

tl;dr those brick tiles with the white trim around the interior of the Castle walls? Those are settlement objects now :D Finally, you can expand and rebuild the floors of the Castle the way they were meant to be (insomuch as the uneven ground will let them show through, anyway)

https://steamcommunity.com/sharedfiles/filedetails/?id=3785227855