Do you have a framing carpenter or are you doing this yourself? A framer will be intimate with the job at hand. If the gabled end on the porch is at a right angle to the existing ridge on your home all you'll have to do is determine the ridge height and bring it back level to the existing decking from your last two commons. Block between the house commons beneath the decking and fasten when attaching the ridge and the jacks. Once completed you'll end up with valleys on either side. Then paper, flash, and shingle. I'm sure at Home Depot or Lowe's you can find a book on framing. Cutting rafters is simply basic Geometry. See ya, Kelly

I'd recommend posting this in the remodeling forum.

Here are some house styles I like... Ours is obviously smaller and we have less money than the people in these houses!

If you incorporate the existing garage closest to the house as a porch, then, if you add your two car garage with its door(s) facing the same direction as the door of the house -- not the direction of the existing garage door(s) , you could also extend the right wall of that garage several feet in front of the existing garage and create a shelter/overhang over the existing garage doors that lead to the front porches -- the one created from the existing garage adjacent to the house that could be connected to the smaller portico at the front door of the house. Driving in, you'd not even see the remaining garage door behind the new 2-car garage. You could connect the two garages with a door. If you like the style of your home ... if you want to keep true to the original design of your home, contact an architect to design your porch and garage addition. Putting up just any porch roof or even a smaller portico roof might not turn out as well as it could.