Help! How to delete single floor tile?

Im sorry I know this is an old topic but I am currently running into this problem where I want an open foyer. I have found that if you make the room downstairs (all enclosed) select the room and go up a floor you can delete the ceiling like you can the wall. Just click on the "room" (its only an outline at this point) and it will give you the delete ceiling option then delete any walls you needed. Just another option of how to do it.