I've built a couple. Each has been "unique". The first one was a 6x8 with an old pop up camper trailer bolted to the side. Light enough where I could tip it over onto the wheels and hook up and go, with the truck or ATV, and then tip it back up when I got to the spot. Worked awesome. I had a central hole with door on the back side of the house from the trailer. Could fit 4 people easily, 5 if needed. I heated it with a Nu-Way vented propane stove.
The last one was an old gas shack from the patch. I think it was about 5x7. 2" thick walls were fiberglass with a layer of insulation in between. Heated it with a bic lighter haha. Door was set in already when I bought it, it was on the side. Hole went on one end of it and had a good amount of room for 2 guys, but wouldn't want to try 3. Light enough and small enough I could tip it up into a pickup bed and move it around. If I had more time to spear, I feel like that was close to the ultimate lightweight permy house. But no time, so I sold it.
Building out of wood, weight adds up very fast, especially treated wood for the floor. If I built another one, unless I was for sure going to have 3 or more people in it most of the time, I would go as small as I could for 2 people. Probably a 4x6 or so with hole on one end and door on the other end. Fold up chairs so you can take one out if by yourself and have more room. Heater is kind of an issue with that setup. I'd probably go with a small buddy heater mounted higher up on the wall with a small battery fan above it blowing hot air down.
If you want to bring a bunch of guys out for a day, buy a clam 6pack (or similar) pop up house and spear out of that.