No matter what structural material you build with, be it steel, concrete, or wood, water is the enemy.  

The basic idea of a rainscreen is to have an exterior surface – a cladding layer - that breaks the force of sideways, wind-driven water movement, so that any water which gets through the small breaches in the surface has lost its momentum.

A report by the Metal Construction Association (MCA) found that 55% Al-Zn coated low-slope steel standing seam roofing systems suffer very little corrosion if properly maintained.