Beavers use logs, twigs & branches, stones & mud to build their lodges and it's that combination that makes for a strong reinforced beaver home. The mud is used similar to the cement utilized in human construction. It goes on wet and then solidifies, reinforcing the structure.
However, unlike human construction, beavers only have the tools literally at hand (or foot or tail) to collect the material, transport it to the building site and then make their way up to the top levels to complete the tasks.
Obviously, the transportation is probably the easiest step, literally ferrying the logs & branches across the pond but there are no chainsaws, cranes or heavy equipment to assist in the harvesting or the moving of heavy boulders & rocks up to the top of the lodge.
And I can say as a meager human, it would not be possible for me to carry a log or a huge boulder up a slippery muddy slope, having extracted oneself out of deep water. And then, of course, there is the matter of a four legged mammal balancing itself on two legs and walking, let alone climbing to the top of a beaver lodge with a heavy load. Extreme human athletes should take note.