Changing floors in construction mode

[The Ugly]

My friend and I were playing Co-op and the construction mode tutorial showed up with controller controls. Now when I try to construct with mouse and keyboard, I can't figure out how to change floors. Is there a key or shortcut to change floors in construction mode?

[The Bullet]

There's a button at the top left of the screen.

[The Ugly]

I'm not seeing a button in the top left; there's nothing to the left of the walls/furniture toggle.

[ricky.d.keim]

in case you haven't figured it out yet it's that Tall Rectangular Button and you need to click the top of it.

[Doombunny]

that is not intuitive at all