Personally, I'd leave it. I know that copper oxidizes with exposure to air and water, so maybe the slope of the roof explains the " unevenness" you see...the lower part getting more contact with water. But that is just a total guess. That said, it's just what copper does, and since it doesn't harm the metal, I would just embrace the natural patina for what it is- after all, they don't make the statue of liberty shiny copper again or paint it black.;)

Leave it...it's patina and part of the charm of a copper roof.

Oh please don't do anything to your beautiful copper! It's doing exactly what copper is supposed to do.

We chose a color for ours that resembled the patina of copper, without the wait. You can get chemicals that will hasten the color change to verdigris.