Gable roof with an uneven pitch

[TanyaSmith]

Hi,

 

I'm trying to recreate an uneven roof pitch (if that's what you call it) in Home Designer Architectural with a large dormer (almost a cross gable roof), but the roofline on the main part of the house keeps centering itself when I add the large front dormer. The first photo is the house I'm trying to recreate. The second image is of the roofline I am trying to keep (the roof is longer at the front of the house), but when I add the dormer, the roof changes to what you see in the 3rd image. 

Can anyone give me a hand here?

Thanks in advance,
Tanya

[TanyaSmith]

I'm using Home Designer Architectural 2018.