There are several scientific publications about the comparison cool roof / green roof and on the question of protection against heat, the cool roof is at least as effective or even more than the green roofs (cf. http://www.sciencedirect.com/science/article/pii/S0378778815003527).

Knowing that these studies are based on cool roofing technologies much less efficient than the Cool Roof France coating. Then comes the important question of ROI, because the green roof will cost much more to install, may require a revision of the frame because of its weight, and assumes a consequent maintenance.