Sorry, not sure of the actual term. See:
In the foreground is a ground floor extension I will eventually connect to the main house.
On the left is a shallow pitched lean-to roof. On the right is a room-in-the-roof.
I drew the roof in the roof first, then pulled up the edge to form the shallow lean-to.
The problem is the extra angle introduced when moving the edge to form the shallow lean-to roof. There should only be three roof faces. An extra edge was introduced on the roof between the shallow roof and the room-in-the-roof.
Sorry, this stuff is hard to explain (for me without the vocab).