Sort of built my own, - one layer of sheathing, two layers of R-Max, with offset seams, all taped with some serious 30-year-minimum tape, then foamed all edges and interfaces, and vent pipe incursions, then another layer of sheathing, more sealing, and then EPDM over all of it, sealed on all edges.
Also used BIB (Blown-in-Batt) inside the rafters.