All three pyramids were built during the Third and Fourth Dynasty; these structures resulted from a monumental effort by the king (and his sons). The Pyramid of Khufu has a base which covers roughly a nine acre area (approximately 392,040 square feet). The Pyramid of Menkaura, unlike the other pyramids, has granite covering one tier of its base. The Pyramid of Khafre had a two-tiered base encased in granite.
Unfortunately, like many of the great kings of the Old Kingdom of Egypt, the Pyramids of Menkaura, Khufu, and Kafhre were not finished by the end of each respective king's reign. As an example: in the case of Menkaura, the king died before its construction was completed. The monuments of Giza and the entire Giza Valley stand as a marvelous reminder of the skill executed in the creation of the pyramids, and are truly fabulous to see." - in: http://www.mnsu.edu/emuseum/prehistory/egypt/architecture/gizapyramids.html