Imagine the following situation:

A group of friends found a remote spot in a state or national forest that they really like. They keep returning to the place quite often, lately there are at least some members of the group staying overnight at the spot at least once or twice a month. They established a fire ring, surrounded by rocks, and someone dragged few logs around the fire to sit on. They have a rope strung in the trees to hand their food from. 

Now some of them have an idea that it would be nice to build few camp benches instead of the logs, and perhaps some primitive wooden shelter. It is clear that there is some sort of limit, they clearly cannot go and build a large log cabin there. There must be some sort of limit between few logs around a circle of rocks for fireplace and a cabin. I am wondering what would still be considered OK, and where one would cross the limit.