Cannot place Roof on custom building

Trying to place a roof on a simple 1 story building and no matter what I am doing its coming up red and deselecting the building.

Ended up being able to place the roof but now it has no sides, I had to save it, remove it then rebuild it. Seems that after setting it to build you cant add anything more to it

That is correct, there isn’t a “waait staaaahp I forgot something” button currently