I would ask your county building code department on the required height. If there were no minimum, what height would you use then? Most of PA uses the unmodified 2018 IPC, but the unmodified 2018 IPC is silent on that.
Maybe look at other roofs, including new construction, and those might give you a good indication. If your vent is going to be on the side of the roof not visible from the street, then your concern about what it looks like should be less significant. Regular PVC should be protected against sun. Latex paint is one way. I might use 2 inch gray schedule 80 plastic conduit. I think it is treated for UV.
https://ecode360.com/32022076 says 12 inches for Township of Warrington, PA.