It is a little known fact that you can make your own fire pit bowl to sit around on nice summer evenings. With a few materials and some space, you can design a fire pit bowl that will decorate your backyard while providing a nice place for a crackling fire.
Lay out a tarp that is at least 10 by 10 feet square onto the ground. Mark a circle that is at least 36 inches wide with a permanent marker on the tarp. You want to be free to work without worrying about making a mess. Pour out a bag of fine sand on the middle of the tarp. Add enough water to make it stick together like beach castle sand, and start mounding it up.
Open another bag of sand, add water and mix with a hand trowel. Pile this wet sand on top of your original mound. Mold it and smooth it into an inverted bowl shape that is as wide as the circle you marked on the tarp. Continue to add wet sand until your mound is as big as you want your bowl to be. Cover the whole thing with a plastic sheet to keep the moisture from evaporating.
Prepare your concrete by pouring it into a wheelbarrow and adding the water. You will use a couple gallons per 50-lb. bag of concrete, but add it a little at a time so you don't get it too wet. Mix it thoroughly with a hoe until there are no more dry spots. If you plan on making very hot fires, you can use a refractory concrete recipe at TraditionalOven.com (see Resources below).
Mold the wet concrete over the mound of sand. You will want it to be 2 or 3 inches thick for strength, so mix enough concrete for your size bowl. Keep the wet concrete covered with plastic sheeting between layers. While the concrete is wet, insert several straws through the top of the mound. This will allow rain water to drain.
Place a board on top of the wet concrete. Use a level to make sure you have a level, straight base for the bowl to sit on when you invert it. Turn the level in several directions to make sure it is level all the way around.
Allow the mound to dry for 48 hours, but make sure it stays covered with the plastic so it doesn't dry too quickly. Lift it off the sand mound. Remove the straws and sand it down to your preference.