Catfish, the steel itself isn't that much heavier than aluminum piece for piece (1x1x16ga. vs 1.5x1.5x.125 alu). Also plywood is about the same weight as a .125 sheet of aluminum but a heck of alot cheaper. The main way you would save weight by using aluminum is by using less bracing and using the top as part of the structure. For the weight savings is it worth the extra cost? For me when I built the deck NO, but someday I would like to go all alu. anyways.