15 years ago, I built an extension on a barn stall to suit my wife's draft horse.

I am not a carpenter.

I was not trained. I had no experience.

What I had was Home Depot, and I'd seen enough framed work and enough videos about people building buildings, and the belief that I could "figure it out." Also, this was a barn in rural country, and people wouldn't be living in it so I wasn't too concerned. So I bought a Saws-All and cut a giant hole in the side of the barn.

Long story short, I did figure it out, and it wasn't half bad. Framing the roof gave me the most trouble; I kind of understood the theory, but I had the feeling it wasn't as neat as it could be; it was the only part of the project that required joining. It had proper siding, a proper roof (with some composite corrugated roofing), and even a ventilated peak with corrugation foam under the top-thingy to frustrate wasps. It had a big-ass sliding door, which I bought pre-made. It had a12" ramp from the door into a paddock made of packed 3/4-minus (second hardest thing). The inside, like the rest of the barn, was just 1x4 horizontal planks, stained, which made everything easier. It didn't need to be fancy, and the ceilings were all open, so no ceiling work.

In the end, I learned several things:

1. Home Depot has everything you need to build a small house, including truck rental to get the material to the house.
2. I waaay overbuilt it, out of paranoia that I would under-build it. I had double supports every 16" and horizontal cross beams. Like the rest of the barn, there was no floor - it was all packed 3/4-minus - but I poured a 1'x3' concrete foundation over basebed gravel for the walls. I'm not certain anymore that the original barn had more that 4x4 posts sunk in concrete. I believe that, had I been experienced with building, I could have done the job with far less material.
3. Home Depots wood is absolute shit. I screwed double 2x6s mainly to try to get the damned things straight enough to build on. And I bought only pressure-treated wood because I wasn't certain that my siding job would be perfect, but also because this was open to the elements.
4. I learned to hate Phillips-head screws with a passion that's lasted the rest of my life so far.
5. Someone with no experience can do something like build a glorified shed. A 14' tall, 16x16, sided and corrugated roofed shed, but a shed.

I was pleased with the result, and I'm grateful for Home Depot because there's no way I could have done that without them. Not within the season of weekends that it took me.

The only wood I'll buy from Home Depot is unfinished shelving wood. Their shelving stuff is outrageously expensive, but it's clean and straight, and properly cured.