Removing a single tile of roof/floor?

Basically I’m trying to remove a single roof tile on a building to let a sliver of light come through the ceiling.

I have access to the roof, and I have a pickaxe/jackhammer. I’ve read around online about people able to destroy floors, but I can’t find any way to. Activating the pickaxe does nothing, and neither does smashing with it.

Have you tried ‘dig downstairs’ from the construction menu?

For what you describe and intend to do, no. There’s currently no in game way to add a poor man’s skylight to a house.