Rust on a roof can be effectively controlled with mechanical removal and the use of specialised primers.
Start by ensuring all the rust including any loose material is removed by abrading with sandpaper or by using a . Use to remove all grease, oil and rust residues, then flush with fresh water and allow to completely dry prior to priming.
Once the rust is removed, you can apply Then when the primer is dry, use .
For areas where all the rust can't be removed, apply , which is both a primer and rust convertor in one. The primer can be applied over hard to remove rust sections, sealing them off from moisture which will prevent it from continuing to corrode. - MitchellMc