Not at all green -
Steel studs are killers on insulation. They can reduce an R19 insulation (theorhetical "pink-not green" lab test) to an effective R11 wall. The heavier gage studs could have even worse actual thermal performance.
Cement does require energy, but is generally relatively local. Aggregates are also local and do not represent a large amount of energy. Deliverly and distant transportation associated with iron ores, processing and delivery of finished steel products are very big factors when looking at the big picture.
A different approach - As backward as they may be in some areas, China has abandoned both wood and brick as "green" materials in favor of of concrete masonry because of land preservation, continued use of arible soil, pollution, energy to produce, transportation and constructability of an energy efficient residential structure. This started abo 10 years ago, and the old inefficient polluting brick plants are being phased out to preserve the land and soil. - Not a small job since China uses 525,000,000,000 brick each year(500 per person) and they now import wood when necessary to preserve good soil. I don't think ethanol has a good future in a country with over 1,000,000,000 people.
Everyone has their own idea of the factors in what is "green". The concept of building out of waste materials is good on a small scale until people realize the waste has value if there is a demand. - I remember when fly ash was a waste product and people paid to have it hauled away and dumped.
Dick