You can join roofs to other roofs or walls, or unjoin them if they were previously joined.
You can join a roof to the top face of another roof and the wall below that roof if you select the wall as the target. The wall must be attached to the target roof and the target roof must be a footprint roof. You cannot join a roof to more than one top face of another roof.
Note that you cannot add the second roof by editing the sketch of the first.
To unjoin roofs, click Modify tabGeometry panel (Join/Unjoin Roof).