i have like white crusty looking stuff on my roof =/ is that it?

 

If you have tried claybar, waxes and compounds and the oxidation is still there then you will need to wetsand it out and machine buff the clear. I would start with a real fine grit like some 2500 if you can find it. Get a soft sanding block and soak it in clean water with the paper for a few hours. Then get a spray bottle and fill it with clean water. Wash your car very well and park it somewhere were crap wont fall on it while you work, like in a garage. Wrap the block in the paper and sand lightly in an x pattern keeping the surface and the paper wet with the spray bottle. Do not sand over body lines, stay about a 1/4" away from them. Use a small squeegee every once in a while to clear off the surface and check your progress. Once you have the surface sanded and the oxidation removed to your liking, get a buffer with a wool pad and some cutting compound. Make sure the surface is clean before you buff. You may want to wash the car again. Buff the surface at a low RPM until the dullness is gone from the surface. Then get a foam polishing pad and get some machine polish and polish the surface at a slightly higher RPM. Once you have restored the paint to a nice deep gloss, get some hand glaze and a microfiber towel and using only a dime sized drop per panel rub the glaze on in a circular pattern all over the panel until the glaze is no longer visible on the panel. After each step (compound, polish, glaze) you will want to wipe the panel clean with a microfiber towel before you move onto the next step. Once you are finished glazing, you will need to clean the car good and remove all compound and polish from anywhere it got on the car in the process. You want no compound left on the car because the longer it stays on, the harder it is to remove. Its a good idea to give your car a good detail just to be sure. Now wait a few days and wash the car again and apply a good wax.

 

Nice sources here