Which waxes or polishes work best to restore severly oxidized auto exterior finishes?

I recently bought a used car, and paint job and finish are nice on sides but very oxidized on roof and hood areas. I was wondering if there are any certain waxes, polishes, or chemicals that work best for restoring severe cases such as these. I have tried a few top brand waxes, to no avail. Any help or suggestions on this matter, would be greatly appreciated.