recessed gable roof

[Dan Park]

If I am understanding the question correctly this can be done. Make all the walls full gable walls including the bump outs. You should not have to make a wall the entire length of the house.

Next delete the roof and rebuild it.

For your recessed area try using a railing or an invisible wall. A deck area by default does not build a roof a porch does. Make sure you label your rooms correctly or check the roof over this room in the room specification dialog.