Wasn’t checking your work, just getting a sense of the size. You’re about 6 months ahead of me, living my dream. I do not have my footprint determined yet. I like the depth of your shop.
I want to put a small living quarters on the back of my shop. Not really to live in, but maybe spend a night or 2, clean up, fix some food, nap, ………
I went back-and-forth, round-and-round deciding. My dad and BIL had a 30x50 pole barn built years ago, 6x6 posts, site-built wood trusses on 5' centers. It originally had a dirt floor, but later they had a slab poured. It has a 10' door in the middle of one long side. So Dad's Ford 3930 with 6' brush cutter backed in with the tailwheel in one corner, and my BIL's Ford 1520 with a rear mower fit in with room to spare. Recently Katy, my L35, relegated the 3930 to my sister's 'unused' horse barn hall. I don't think she appreciated Katy's drips.
I'm building in north Mississippi, so no real frost or snow consideration, and no local code for a non-occupied building. My thoughts:
* I knew I wanted a finished floor, so why not pour it first and have a flat work surface? Also avoids wood in ground contact.
* 30' width has held everything we need so far, and I could duplicate the trusses we have if I had to, although they're crude with overlapping joints, etc. 30' - 32' long wood trusses are pretty economical. 32' would have saved a little material waste.
* 60' length 'cause that fit. I started out thinking maybe 80', but when I got the site cleared, it turned out that 60' fit better. I don't have a definite use planned for that area, so it should be plenty. Using a 4' module makes for more efficient material usage.
* Stud frame/wood siding. Here the logic is a little fuzzier and I may have long term regrets. I won't have wood in ground contact, and 3/8" LP SmartSide siding can be applied directly to 16" stud spacing. If I need to add a door, it'll be pretty easy with wood. I think I could have used 4x4 studs on 4' centers with girts to use metal siding.
* Insulation. I don't plan to install insulation right now, but I should be able to install batts in the walls and foil-back sheets under the roof if I decide to insulate.
Good luck with your venture. I thought about living quarters. But, for me, it would have been a place to live until I built a house. So I would have wanted a bigger space, plus any walls, finishing, etc. would have been throw-away cost. And finally, the whole shebang would have to meet local code.
I think I'll come in at around $40k. We'll see.