When I was eleven or twelve, I don't remember for sure, but I was still in elementary school, which ran through the eighth grade when I was in school, my cousins and I camped out in a variety of structures that we built ourselves. This included several shacks made of new lumber and materials, one of which was a two-story structure, brush huts that we made out in the woods, and a teepee-type structure made of all-natural materials that could be found in the woods where it was built. That one was built for our Camping Merit Badge in Boy Scouts, and we spent two days and nights in that thing in a Michigan February, and were relatively comfortable, at least when we were inside. Although much of it was made with birch bark, and all of it was built from combustible materials, such as logs, branches, and twigs, we had a fire in there. I suppose there may have been some danger involved with that although, in case of a fire, we could have exited from pretty much any wall of the teepee. But the one that I had in mind for this thread was not that. We built another domicile from an old pigpen on the far side of one of my dad's pastures. The pen hadn't been used for pigs since before any of us were born so there was no pig debris remaining. The pen had been built into the ground so only a small portion of it could be seen from above ground. We repaired some of the bad boards that were on the pen and dug the floor out so that we would have more room inside of it, resulting in a place that we couldn't stand up in but we could sit or kneel and still have some headroom to spare. When it was deep enough, we built a wood floor and extended the wooden walls to reach the now lowered floor space. The school district had dumped a whole load of books at the village dump so we rescued a bunch of those, and built a library into one of the walls, and used some of the books to get fires going. Also at the dump, we found an old woodstove. It was a small one that had probably been used in an ice fishing shanty, so we added a chimney using a stovepipe that one of my cousins dug up somewhere. There was only one entrance, and it was just wide enough to crawl through. It was more like a doggy door than a door, and we had a thick towel hanging over it to act as a door. There was also a block of wood that we'd use to close it more securely when we left. We shoveled dirt and used some brush to conceal the only part of the structure that could be seen above ground. We did have some air outlets with screens in them that we thought might reduce the likelihood of snakes or nasty bugs finding their way inside of our home. It was a little claustrophobic in there, however. Other than making sure that it worked, we didn't have a fire in there during the summer because it took only moments for it to become stifling hot in there with a fire going in the stove. However, we spent some nights in it the following winter. Even in below-zero weather, we needed only the smallest of fires in that stove in order to keep warm. If anything, it was uncomfortably warm inside. A candle was almost enough to keep us warm. As far as I was aware, neither of our parents knew about this place or most of the other places that we would build. My dad visited the two-story shack that we built, because that wasn't far from our house, and was pretty impressed with it, although my cousin was the architect among us.
We used to build "forts" in the woods behind our home. They were on property owned by an old lady (Mrs. Sisk) who lived in a shack off of a logging road separate from where the regular folk lived at the paved street. Part of her property was a strip between our property and the train tracks (The Washington and Old Dominion Railroad, which has long since been converted to the W&OD Biking Trail.) Those forts provided cool places for us to be in the hot & humid DC summers. Every once in a while her adult son would visit her, and he would destroy our forts. We'd just rebuild. She never said anything to us directly. In fact, I'm not certain I ever saw her up close, but I do recall her shack and her chickens. $1,000,000 homes now sit there.
I was related to most people around me but we never gave much thought to who owned the land upon which we built our shacks. If it wasn't someone's yard, it was fair game.