A Decent & Non Perishable Metal Roof Paint?

[David Shellman]

Hi All, I have tried many roofing paints on my garage's galvanised sheet roof over the past 25 years. I started with a metal paint on top of a red oxide primer, since then I've used bitumen paint, and then Isoflex - which promised to last 15 years but has now perished under the sun within 5 years. No matter what I use, it perishes and the original green metal paint (along with a few rust marks) show through. Can anybody recommend a flexible paint to go on top of the remaining Isoflex? Many Thanks.

 

[Tigercubrider]

Galvanisation makes adding paint difficult.