How do you delete a roof?

[LittleBlueDuneBuggy]

I'm trying to build a second floor, but the walls say they're intersecting a roof.

[LittleBlueDuneBuggy]

nvm. I figured it out.

[Nibbibara]

To remove an existing roof you must left-click the roof in question to get the blue wire frame appearance around the building. Secondly, you right-click anywhere on the roof to bring up the radial menu and select the option "Destroy Structure." If done correctly the building will be roofless.