How did the Inca complete building projects?

The short answer to this question is that archaeologists are not certain how the Inca built the massive temples, buildings, and roads that they left for posterity. In particular, it is unclear how they performed the calculations necessary for such projects, since they had no written language and did not use the wheel for transportation. The Inca used dry stone building; that is, they did not use mortar to hold stones together. Rather, the stones were hewn to very precise specifications so that they fit tightly together, and there are many theories for how this was accomplished. They also used fired adobe bricks. The one thing that seems certain about Inca building techniques is that they required a great deal of manpower to undertake them. Thousands of people were involved in quarrying, transporting, and fitting stones, and many more worked in other capacities in building projects. This indicates the extraordinary power that Inca leaders wielded, as well as the sophistication of the Inca bureaucracy.
https://www.pbs.org/wgbh/nova/inca1/qanda.html

https://www.rediscovermachupicchu.com/mp-construction.htm