Hi Trista! My FAVORITE book on how they did it, The Pyramids: An Enigma Solved, by Joseph Davidovits, a geology professor & specialist in synthetic rocks. All those giant blocks, not quarried in cubes, but set from limestone rubble like concrete. To quote one of his arguments, Why are the Great Pyramids 20% lighter than the limestone in the quarries where they came from? Forget about still undiscovered secret passageways. Anyone who's ever poured concrete knows about air bubbles.
So much more, & all absolutely scientifically sensible. Your son's social studies class will never be the same!
Anyway, I really recommend it -