I am not sure if this is the right forum. Hypothetically is there a natural building style that can be completed independently? For instance I know I am not capable building a log cabin on my own but could a person build a cob home alone? I am just wondering out of sheer curiosity!
The next question would be why would you want to? If you are building a little hut to work on while you develop a property that would be ok, right. But if you want a house that will last hundreds of years, the whole point is to fill it with people. The point is that it fits within a larger community. I just heard about CEB or ISSB, which are compressed bricks. I guess you could build one on your own. You could build a cob or wattle a daub house but if you are going to dig up the dirt with a machine someone else will probably be helping if not at least to deliver something. I think a more interesting question might be to ask how many different people can you get involved in building a house.
With enough ingenuity, there isn't a style of natural building that couldn't be done single-handedly. Yes, even a log cabin. Obviously in that case the challenge is lifting really heavy logs into position. But all you need to do is figure out how to multiply forces and use mechanical advantage. You can do a lot with a come-along and a few pulleys. Of course, everything will take longer. Some things might even take more than twice as long as if you had two people.
In response to Scott's question, "why would you want to?" I love building alone, especially on my own projects. I like not having to communicate what I want done, and then looking over someone's shoulder to make sure they know what they're doing. My thoughts get very muddied and I feel lots of pressure trying to organize people and keep them busy. I really enjoy the slow pace of thinking things through on my own. I also enjoy the challenge of figuring out how to do alone what may seem impossible. Or maybe you are building alone out of necessity, without the money to hire help, or maybe there are no other people! Whatever your reasons, I think there is a tremendous sense of accomplishment and satisfaction in looking at a building you have created all on your own, no matter how hard or easy.