Using shovel, remove 3 in. depth of soil from the entire circle. Tape the level to the narrow side of the 2-by-4; use the board to level the surface.
Fill circle with 2 to 3 in. of sand, rake smooth, then recheck the overall level.
Moisten sand with water, then tamp it firmly. Level again.
Place the stones
Starting at the outer edge, position the large stones to sit slightly above the surrounding soil surface.
Arrange as carefully as possible for fit; place as many large pieces as possible, then fill in with smaller pieces.
Check the level of the patio regularly.