It has what seems like 1" square tubing and the sheet welded to it.
If you haven't already purchased it, I would ask to find out if they know how much the dry weight is, and get an idea of the steel skinning thickness, just in case it comes down the need for cutting out holes for doors, windows, etc. If it's heavy steel, like 1/8th or more, I couldn't see any use in something less than a torch, or plasma cutter to make your cutouts.
Take a close look at it, if you can, or ask lots of questions, with some kind of idea, or plan in mind. That will help you figure out if it's something you want to dive into. Of course you can always just bombard with questions, and post them up here. There's someone here that can probably give sound advice on any details that you post up about it.
At first glance, it looks awesome, with so much there to start from, but it's starting to sound like a pretty daunting task, in my opinion. Not to sound discouraging though. Anything is doable, and that is still a pretty awesome spot to start from.
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