What design would you use to build a pyramid with the largest interior cavity, only using primative methods?

The design i was thinking about was a half oval (with 4 arches), with the open end down, and the pyramid built around it. The design should be structurally sound, and the construction materials used are only stone (like the egyptians). No current-day technologies can be used. Thanks for the help.

What design would you use to build a pyramid with the largest interior cavity, only using primative methods?
The big problem with your solution is that arches are not a contemporary technology - they came into existance long after the pyramids were built. That is why the chambers in the pyramids are relatively narrow and long, so that rock slabs could be used to span the gap. Some places used a kind of shelved over hang, like pushing a deck of cards to one side, to make a raised roof, but no balancing as you would find in an arch.