It is a steel tube building, all of the tubes are 2.5" galvanized, the tall walls are double thickness tubes, the roof trusses were a thicker gauge, welded and the welds covered in a cold galvanizing to prevent rust. I don't remember the actual gauge of the tubing, but the wall tubing was a little over 1/8" thick with the tall walls being two of those, one inside the other and the roof trusses were a little over 1/4" thick. We have been hit with 50-70 mph straight line winds with zero issues, winds that destroyed many homes in our area, this building is incredibly strong. We chose 3/8" PlyBead for many of the interior walls as it adds racking strength.
When we started looking for a material to do this I naturally went to wood as my career was in mfg. and distribution of lumber and building materials. I could not frame both buildings in wood for what the metal building cost. We paid $70k for a 24x24 guest house and the 40x70 main house, both with 14' walls and that price included dirt work, 6" slabs and plumbing in the slabs. That was 2014, things are higher today of course. The main house living is 40x50' with a 40x19 garage/shop, the main house has 2 masters, the downstairs is 16x30', his/her closets and laundry. Upstairs is 30x50', with the master there being 12x30, there are two smaller bedrooms upstairs.
I have over 1,000 pics of the build, I did everything except put up the metal building, ceiling drywall and the 6 tons (8 zones) of mini splits. I did all of it with battery powered tools, we could not get elect until the houses were almost finished.
Here is little video I made for a friend on the West coast who was curious. I have a huge thread on Tractorbynet that details everything but you have to register to see it, who has time for that? lol