Shelters are the most common type of structure and can be found almost anywhere. There are many that have survival skills such as hunters, military and Boy Scouts.
Debris shelters are often the most common of all structures found in the forest. These are A-frame or double lean-to. They can appear in a variety of ways and do not always appear uniform.
Brush shelters can be quite dry and comfortable. Note that they do not need to take a specific shape.
The site I referenced, Survival & Self-Reliance Shelters page shows several styles of shelters. Keep in mind these shelters don't all look like the diagrams and photos. Not everyone takes the time to remove all the limbs from branches, etc. This is why so many perceived structures are seen as chaotic or rather, less uniform.
Many tepee structures will have logs that seem to be too heavy to move but after a certain amount of decay they soak up water just like a sponge so will be heavier than when freshly fallen or end of summer. Sometimes they may be put up when dry and when discovered may be saturated making the logs much heavier. Many good starts to a tepee structure will be a couple of fallen trees against one or two live trees. Keep in mind not everything is moved by one or two people. Boy Scouts for example can move some large logs if needed. Remember basic engineering?
I hope this clarifies some questions about many perceived Bigfoot structures. While it does not explain everything you will see in the forest it does explain many structures that have been attributed to Bigfoot.