Ok, so say for example I had a brick. Could I take the base color texture, and in photoshop, play with the hue/saturation modifier till the texture appears very white (because brick has a very rough surface), and that would be my roughness map? Could this method also be used on all textures?
Ah man, this sounds more confusing than I thought. So everything about the roughness texture will have to be created from scratch? I understand not to reuse different roughness values for different materials that don't match up. Edit: Ok, I'm starting to get it now. The roughness can't be an exact copy of the base color…