[longerthoughts]

>steel / aluminum construction is dropping in price every year

I'm not sure this is any better. Steel and aluminum production are both incredibly stressful on the environment. Brazil, for example, mines massive amounts of iron ore (for steel) and bauxite (for aluminum) in the Amazon, contributing significantly to the deforestation there. I don't know much about the process for steel production, but aluminum smelting is incredibly energy intensive. The result is large energy projects which themselves impact the environment. Hydroelectric dams are commonly used to supply the energy needs and can result in massive environmental side effects in places like Brazil. A common alternative to smelting near mining operations is shipping to countries like Iceland, which has exceptional energy production capacity thanks to its many renewable sources (like hydro) and offers cheap energy. While dams in Iceland have significantly less flora and fauna to disrupt, you're adding the emissions cost of shipping.