Not exactly the same, but I'm in the middle of erecting a building mostly by myself (CF, not red iron). Was engineered, permitted, and parts pre-fabbed. While it's a fair amount of work, it's nothing that somebody with some time, tools and general knowledge can't accomplish.
Mine isn't quite as large as what you're talking about, but working eves/weekends I have it mostly framed after a few weeks. Only offering this to you to not discount the DIY approach. YMMV based on your confidence in your skill level, of course.