Steel retains heat. Aluminum does not. A finish must protect steel or it will rust. Temperature changes cause expansion and contraction.
Steel roofing panels expand when they get warm and contract when they get cold. This constant movement of the panel will eventually cause several problems. On this 10 year old steel panel roof, screws have been worked loose from this expansion and contraction, resulting in leaks. Aluminum Lock Shingles do not work loose from temperature changes.
All steel roofing panels have raised areas or “ribs”. In a valley, these ribs hold snow and ice from sliding out. As seen in these photos, eventually the weight of tons of snow and ice will damage the panels, causing leaks.
Aluminum Lock Shingles are low profile with no ribs to hold the snow in the valleys. Snow slides off before it can turn into ice.