
Yes, this can be done but please realize that the only type of standing seam roof suitable for that low pitch is a mechanically seamed standing seam.
in order to support a new PV panel installation on an existing roof with an inadequate supporting structure, I'm building a new 0.5:12 sloped roof structure above the existing 3:12 roof on one side of my building and plan to install a standing seam roof on it up to the ridge where it joins the existing 3:12 shingle roof of the other side. Will I be able to adequately make a water tight connection between the existing asphalt shingles and the standing seam metal roof with some kind of a cap flashing? I'm worried about wind blowing the water under the cap.