Ah yes, Linda is quite right. I think you can assign shading properties "ShadingProperty:Reflectance" for the surface reflection if you use that object. My description previously fits to the buildingsurface:detailed objects which you'd use for say the floor of an overhanging zone (also shading).
Shading surfaces are not part of the thermal load on the
building and though they can have reflectance, they do not really have
constructions such as the rest of the building elements have.