since some people cry about authenticity:
current assumption for most pyramid constructions is that not slaves were used, but professionals combined with farmers, who worked during the time where work on the farms was impossible or otherwise not needed. They were well fed and housed nearby. Notably, near the pyramids of gizeh a whole city was unearthed that seemed to have been only there to facilitate the construction. The only historical evidence is from some greek scrolls, where one has to ask wether they really studied the situation or made some broad assumptions.
None of the discovered pyramids have been found to contain any remains except that of the pharao or important person in question and a few favored ones, certainly not hundreds of sculptors, engravers and worksmen. In fact, iirc, there was some evidence that talented pyramid builders got their own tombs nearby as they died as a token of honor, but I might be wrong in that, the documentary was some time ago.
Lastly, the design. Before the start of pyramids, the mastaba was the burial form for the rich and/or important. Then someone put a second floor on top, to 'show' he was more important than the others. It was basically two mastabas stacked on top of ne another. This got out of hand, you might say, as new rulers would try to outshine their predecessors. As long as finances allowed ofcourse. Do this for several dynasties and you end up with pyramids.