Choose a space for your fireplace that is free of overhanging tree branches, invasive shrubbery or flammable wooden buildings such as tool sheds or doghouses. The space should be open on all sides, including above.
Push the blades of your sod stripper about an inch down into the sod. Strip a circle of sod about twice as wide as you want your fireplace to be. For example, a 4-foot-diameter fireplace requires a circle about 8 feet wide. The fireplace will sit at one of the edges of the circle. The rest of the circle will be the containment walls and hearth.
Push the tiller blades into the soil and twist, loosening it slightly. This makes it easier to dig and manipulate. Dig a 4-foot-wide, 1-foot-deep pit at one of the edges of your circle. This is where your fireplace will be.
Settle rocks into place at the edges of your pit, twisting and working each one securely into the soil.
Stack and settle more rocks on top of this first layer, building higher in the back. The very front of the fireplace requires only the foundation layer of rocks. About one-third of the way back on either side of the pit, start stacking a second and third layer of rocks.
Turn and twist the rocks, setting them firmly against each other. You may need to test several rocks for each space before finding one that fits perfectly. If your rocks are a uniform size and shape, this won't be a problem.
Create a rock wall foundation into the soil at the edges of the circle on either side of your fire pit. Stack more rocks into place, building the walls to the same height as the back of your fireplace. These containment walls hold in the heat and help contain the flames.
Fill the bottom 6 inches or so of your fireplace with sand. This helps put out ash and provides a heatproof bottom for your fireplace.