extending a portion of roof with home designer 2012

[bnelson1958]

I have a long gable roof with a porch extending off the back about center of the house. I built a shed roof over the porch and extending down to one end of the house. I am trying to get the roof to extend further than the default 18" as in real life it extends 4' to cover a walkway in front of the porch. Is there a way to isolate just that portion of the roof without affecting the overhang around the rest of the house.