VDrift lighting, materials, textures

[CrystalH]

I like VDrift's car material and those shaders. Looked only once inside and they seem quite complicated.
How is the metallic or roughness map made ? Is it drawn by hand, generated somehow form others or baked in blender or yet another way ?
Can you tell in short how do you achieve roughness in shader ? So far i know reflection map is quite big, had to be small to make it blured. Is there some filter that samples it multiple times ? Or how does one get a not so detailed reflection, some sort of glossines and not exact mirror ?