Help! How to delete single floor tile?

> @Fischio said:
> The easiest method I've found to get a two story room with a staircase is to do what was mentioned and fence off the flooring that you want to delete so it creates a "room" then deleting the floor. If you simply place the stairs where you want them it will remove the sections of fence automatically and avoid the floor from reappearing.

> If you get missing floor above the room you can fix it by building a room on the floor above, which fills in the flooring. That room can be temporary and deleted leaving the flooring.

I tried this but I'm still having my roof fall into the second floor - despite the fact there are no roof tiles missing above the area I'm trying to clear of floor tiles. In fact, the roof appears indoors the moment I attempt to fence off the area I'm trying to clear of floor tiles - as if the fencing is programming my house to think it's outdoors?

Update: Out of curiosity, I tried other fence types to the one I'm wanting. They're all doing the same thing. Would love to see pics / a guide / vid tutorial from someone who has had the workaround work for them. But then again, we shouldn't be having to go to so much trouble do so something so simple...