You're going to have to  be a

You're going to have to  be a lot more specific to get an answer... How old? Under what conditions? What kind of metal? Pilings? Quonset hut? Mine header? Silo?

elevator

Heres the project im doing.

I'd start with a soft gray,

I'd start with a soft gray, like galvanized nails. Overcoat with a thin raw umber.

Add burnt umber for deep corrosion.

Not the only solution, but it's what I see in sheet steel.

Since galvanized metal

is not monochromatic, I’d use light gray, white, and a darker gray, like pewter. I’d use make up sponges and dab a little of each on sponge and then apply to siding. It takes some practice, when dry you can add light streaks of rust colors, and dirt stains etc.