My Multi-Layer Physically Correct shading in Blender/Cycles starts to be fine for the first tests.
So, I'm trying a standard case study for multi layer : Candy Apple Paint !
I've found the recipe and 'how to' on a street-rod forum on internet, and convert it to multilayer shading : Golden Base(mid) + Dark color(thick) + Clear (thick). It works pretty well !
Of course, the work is not yet finished. I still have problems with node limitations in Blender, and it's currently working just on GPU rendering...
I'm still working on it, and it will be improved and easier to use.
There is no flakes in this paint, as the goal was not to make a perfect car paint, but to use multi layered material.
So, here are the results :