Measure the length and width of the sheet metal to determine the size of the pit. It is easier to build the pit to the size of the metal than to cut the metal to the size of the pit. The size of the pit is the width of the sheet metal and the length of the sheet metal minus five inches. For example, if the sheet metal is 28 inches wide and 36 inches long, then the pit becomes 28 inches wide and 31 inches long.
Measure the size of the pit on the ground, marking each corner with a concrete block. Place the blocks so their outside edges match up with the measurements. For example, if you measured the width from the outside edge of one corner block to the one parallel to it, you would get 28 inches. This way the sheet metal rests on top of the entire block and not just part of it.
Make the shape of the pit by adding blocks and connecting the corners. Measure the shape to make sure it fits the measurements for the pit.
Push the tip of the shovel into the ground as close to the outside edge of a block as possible. This marks the place for that block. Continue to make marks with the shovel by going completely around the blocks. Remove the blocks.
Shovel out the dirt inside the shape you made with the shovel until you dig a 12-inch-deep hole. Add some dirt back into the pit, piling it up so there is more dirt on the front end of the pit than on the back. Pack in the dirt so it is not loose. You want to create a small slope that is no more than a quarter-inch. This puts a slight angle on the fire pit that is not noticeable. Use the level to check the slope.
Place the blocks back in the pit, resting them against the side of the hole. Add a second layer of blocks on top of the first. Place the sheet metal over the blocks to make sure it covers the tops of the blocks. Place a pen on the metal to see if it rolls off. If the pen rolls, chances are so will your hot dogs, and the slope is too high. Remove the blocks, and adjust the hole as needed.
Place one layer of blocks back in the hole. Place glue from the middle of one block to the middle of a second, making a zig-zag pattern. Place a block over the glue so that the middle of the block rests on the seam of the bottom two. Press down to help the glue hold. Repeat, adding the next block beside the first, until you have a second layer of blocks. Skip a block on one side of the pit, so there is a hole for heat and steam to escape. Add a third layer in the same manner, but do not skip a block.
Place the sheet metal over top of the pit when you're ready to cook. Place the metal containers at the back of the pit so that the grease from the food rolls down the sloping metal and into the containers.