Steel buildings are less expensive than stick framed, concrete or masonry block, without sacarficing longevity. Some people don't like the look, but you can dress them up with a masonry wainscot, paint and different wall panels. I've built four in the last few years. Three of which were gym/weight room buildings.
Green building and sustainable are terms that mean nothing to anyone in construction; it's purely a marketing tool. Ask if there is any savings for not being green or sustainable. Haha