Rusting galvalume roof

I have galvalume standing seam roof on a house at the ocean beach. The roof is 10 years old and started showing rusty spots last summer. The roof has never been painted. Originally, it had shiny "silvery" look that became dull after 5-7 years. According to galvalume supplier the paint on the metal coil is only applied to facilitate movement of metal though the press and is not intended to inhibit corrosion (??). I am now told that to extend the lifespan of the roof and to slow down its corrosion, it needs to be painted. However, I am not able to obtain clear recommendation for any paint system that would need to be applied. Metal supplier suggests a chromate-based primer followed by a topcoat. Contractor is of the opinion that paint like this will likely start peeling off in 2-3 years and recommends tar-based coating, adding that it does not look "nice." What type of paint would you recommend? What labor cost can be expected on the 1:12 pitch roof?

Whoever supplied the original metal should be the best at making a recommendation. I am not sure about the availability though of chromate primers for field application. Have you checked into that? Using the advice from your metal supplier, you might also want to check into PPG Kynar Aquatic coatings for field application as well as Tnemec's air-dry fluoropolymer coatings.