"...The king then directed the astrologers to ascertain by taking the altitude whether the stars foretold any great catastrophe, and the result announced an approaching deluge. 9 The king ordered them to inquire whether or not this calamity would befal Egypt; and they answered, yes, the flood will overwhelm the land, and destroy a large portion of it for some years.
...upon which the king ordered the Pyramids to be built, and the predictions of the priests to be Inscribed upon columns, and upon the large stones belonging to them; and he placed within them his treasures, and all his valuable property, together with the bodies of his ancestors. - Al Masoudi (emphasis mine)
If there is any truth to this Arabic legend (based upon Coptic tradition) then it seems that the Great Pyramid would, by necessity, have been designed with (relatively) accessible chambers (for storage of seeds, tools, documents etc for the recovery of the kingdom after the foretold deluge) but also with an inaccessible chamber (burial vault) for the "bodies of his ancestors".
Perhaps there is more truth to this Arabic legend than meets the eye.