Research your state's laws on backyard BBQ pit construction. Make sure that you can build a pit without a permit; if not, obtain your state's proper clearances for construction before you make a pit.
Choose an area to build your pit. Make sure the area is far enough away from your home and other flammable construction like a garage.
Lay the grill in the center of the area. Surround the grill with a single layer of bricks slightly overlapping it. You will lay the grill on top of the bricks later.
Using the bricks as an outline, puncture the ground in the shape of their circumference with a shovel. Remove the grill and the bricks and use the shovel to remove any grass, weed or other flammable materials from the circle until there is nothing but dirt.
Dig 6 inches deep into the dirt area. Pour the gravel in up to ground level, but not above it.
Lay the bricks with the inner rim of gravel. Use mortar to bond them together and let dry. Stack the bricks at least 2 feet high around the gravel.
Place the firewood in the middle of the pit and lay the grill on top of the brick wall. Light when ready to cook.