Dig a circular hole that is 3 feet deep. For a grilling surface that is 3 feet in diameter, dig the hole approximately 5 feet in diameter. For a smaller, 2-foot diameter grill, dig the hole 4 feet in diameter.
Rake the bed of the hole to level the ground and compact the soil by pounding it with a hand tamper.
Layer the bed with 2 inches of gravel. Gravel will provide drainage and a fire barrier at the bed of the stone barbecue pit. Tamp the gravel and sprinkle sand over the gravel to fill joints and stabilize the rocks.
Collect an assortment of large and small rocks of varying shapes. Options include slate, limestone, sandstone, fieldstone, quartz and granite.
Build an approximately 14-inch-thick stone wall around the perimeter of the circle. Using large rocks at the base, slowly build up the wall. Fit together rocks as tightly as possible, thinking of it like a puzzle. Use little rocks when necessary to fill cavities. If necessary, split stones into smaller sizes or shapes using a chisel and a 3-lb. hammer.
Reduce the thickness of the wall by about 1/4 after 24 to 28 inches of height to create a ledge along the inner wall. The ledge will serve as support for the grill grate. Continue the wall another 8 to 10 inches so the ledges sit lower than the top of the wall.
Cut a round piece of non-galvanized, stainless steel mesh to fit inside the pit and rest on top of the ledge, and to serve as a grill grate. Cut steel mesh with bolt cutters or a metal cutting torch. Food can also be placed on or hung from the mesh for smoking.
Cut a piece of plywood to match the outer dimensions of the pit and to fit as a lid. Place the plywood over the pit's opening to contain heat and smoke when smoking.