While the plant surfaces and leaves might be cooler than the ordinary roofing material of a building, the underside of an elevated panel with a tilt (where the cells are laminated to the glass) see very little cooling effect of the sedums transpiration at the cell height due to wind and boundar layer mixing. I’ve run arrays if thermocouples to measure the temp gradient due to localized greenroof cooling and it is a negligible difference. I can share data if you would like. This point was also confirmed by a Portland State study.