Built my 24x30 in 1990, from the bare dirt, mostly by myself. I was 24 and the only experience I'd had was a garage in a HS construction tech class. My wife and I built an 8x12 shed with used lumber a couple years before.
I prepared and poured the concrete floor using little more than a spade, shovel, wheelbarrow and a small garden tractor. Built the concrete forms from 3/4 plywood and 2x4's. Hired an experienced concrete guy to direct the pour and run the power trowel, think he charged me $50 for a few hours work on a Saturday morning. Wife and I bought, loaded and hauled the lumber package from the city about 50 miles to our house. It was complete minus the overhead door. Hired a friend to lay two rows of block around the perimeter to get it off the ground and add a little ceiling height. He worked a couple hours in the evenings for a week, think it cost a couple hundred bucks and the materials.
With the help of my wife we framed the walls, stood them up and braced them off. A friend and my brother in law came by to help swing up the trusses. Got the overhangs framed, the plywood on and the shingles laid, had some occasional help, couple hours here and there but mostly on my own.
Installed the windows, walk door and trimmed out the overhead door then installed the siding pretty much all by myself. Had to get creative to hold the opposite end of 16' engineered siding. I'd support it close, get one end attached then adjust and nail it off.
The cheapest option for an overhead door was to hire it done. I called and ordered it, they brought and installed it. I wanted an 8' x 16' door which was not that common back then. The overhead door company came out a couple hundred bucks cheaper than I could order one from the lumber yard, go pick it up and install it myself. Getting one from the lumber yard would have required two trips to the city to order and then pickup. I was able to just order the door plus an install right over the phone. They didn't even charge tax for new construction. When complete they mailed me an invoice payable within 30 days, boy how times have changed.
Once it was done I wired it, insulated and installed ceiling and drywall over the winter. The basic construction took me just a few weeks of after work and weekends and a couple vacation days. Pretty easy job. Crazy to look at the receipts now, I had it completely done and finished including concrete for about $4500! The lumber package was $1900, had about $950 total in concrete and the door was almost $700. Insulation was like $6 per roll and the drywall was $1.29 per sheet.
I built several in the years following for friends and family. Helped one friend about two years later build the same 24x30, then the next year another friend to build a 28x36 with a bathroom. Then we built his father in law a 28x32 attached to his house, then my aunt and uncle a 24x30. All total I've built ten garages since building my own, only one of those included me doing the concrete. Learned a lot, something new each time and each garage has gotten both better and faster. The last 24x30 a friend and I built for his mom, took 5 days from start to finish and cost was approaching 15 grand.
Trusses come with bracing instructions, I put up every stick of bracing they called for. Garage doors come with 48 step instructions, easy to install if you follow the instructions.
