Help! How to delete single floor tile?

I think I might have found out, how to do that:

First you create a little room 1x1 f.e. and delete the whole rest.
By doing that you can leave the stairs where you wanted them to be,
for it only deletes the floor.

Second, now you can start and spread the 1x1 Room f.e. on the 2nd floor,
in any shape you please.

Do not delete the floor in that 1x1 room,
but everything around it.


Actually thats it.



Have a nice day guys.