I built 3 main ones between the ages of 10 to 13.
1. A large, square roofed shelter with two big Y logs and a bunch of sticks and bark sheets across the top and covered with moss to camouflage it.
2. An A-frame shelter big enough to stand in made of pine, bark, and sticks and leaves. My grand plan was to plant corn here and start a "village" but I needed to invite some friends and everyone else was more interested in videogames.
3. A real fort-fort where I actually went to the length of chopping points on my logs and using a post hole digger to make a row of wooden stakes in a palisade. Then I dug a "bunker" behind this but had trouble making that into anything more than a covered hole. It's actually kind of a miracle I didn't bury myself alive, lol.
I had a few smaller affairs, like a bunch of stick enclosures and a treehouse. I also built several dolmen out of serious stones, one of which I actually had to use a sledge on rollers and a winch to move one of the stones, my dad helped me move it and I am so proud of that memory. It's still out there unless some tasteless asshole knocked it over.
What about you? Share your fortification plans.
Boys will turn a forest into Albania given enough time.