Home Improvement Questions? Ask a Handyman for Answers
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Your best option is to offset the roof lines so the new roof is either at least 12" above of below the existing roof.
A drawing is not available. You just frame a knee wall to accomodate (fill in) the height difference. Since there is no load on this knee wall you can attach it to the existing gable with angle bracket supporting the framing or frame a partition down to the slab. You will have to step flash the (I assume) aspahlt roofing shingles on the existing roof onto the knee wall before you side the kne wall.
Then you have to reframe the side adjoining the additon so it's a gable
Consult a designer or a structural engineer to draw up plans if you need working plans. Basically you extend the ridge to meet the additon's knee wall then fill in the rafters.