How to join roofs with different pitches?

I have a well house with a 5/12 pitch roof (simple gable on each end). I want to put a porch on the side of the well house with the sloped roof. At the intersection of the wall and roof, I will start my porch roof with a 3/12 pitch. So imagine one slope coming down the roof, then leveling off to a slightly less sloped roof the rest of the way (over the porch). How do I do that? I haven't built the roof yet, so I can easily tie into the roof trusses I'm putting up on the well house.