The existing roof pitch is about 5/12. The exterior is vinyl siding and the roof was just put on last year with 35 year shingles.
I would prefer to attach this to the existing roofing (perpendicular) and maintain the existing pitch in the new roof, but this also increases the costs because I get into gutters, more complex framing, de-construction of the current roofing shingles and introduces valley protection on the roof where the two meet. It seems like a whole lot more work than the alternatives.
I'm just looking for a reason to justify this approach over the unattached style.