Talvara gave me an idea for cellars.
1 - Disable building houses in houses because it's a bit TARDIS.
2 - Allow building of cellars in houses (only in houses) make it take a bunch of stone and maybe some wooden boards for supports and work as a ladder/stairs that operates similarly to mine entrances and will take you down to a new room in your house.
Maybe limit to 1 cellar per house room to stop things getting too crazy