
I unfortunately do not have any suggestions for you. However, I would caution you that coating on top of the roof will likely void any warranty on the roof. Over time, with natural dirt accumulation, the gloss and sheen will diminish. Think of leaving your car outside and not washing it ... over time, it will stop shining.
We installed a standing seam roof about year ago on a home in Kauai. It is rated as "low sheen, low gloss" but the neighbors are up in arms that there are times when the roof is very reflective. We would like to appease the neighbors if we can, and are curious if any has any suggestions as to whether and how we could possible coat the newly installed roof to further reduce its reflectivity. Thanks in advance. My email is barnheim@gmail.com