Knead a 6-inch cubed block of moist, prepared clay on a smooth wooden board to soften it for molding. Measure out a quantity of fine, white sand equal to one-third the volume of the clay. Add sand to the mass, working it thoroughly into the clay. The sand will give the clay tile extra strength.
Mold the sand into the shape of your roofing tile. You can use a commercial mold or create your own from household materials, depending on the shape you need. A simple, curved tile is easy to replicate with tin cans as a mold. Make the tile about a half-inch thick.
Poke two holes on the top of the tiles with a stick for the nail holes, matching the placement of your roof tiles.
Set the molded tile on a board and set it outside in a sheltered area to dry completely for about two days. When you feel the tile surface, it will no longer feel cool when the moisture content is low enough for firing.
Build a fire outside in a fire pit or even inside in a fireplace. Lay down the paper, the kindling and then several pieces of split hardwood. Set the tile in the middle of the stack, within the kindling. Light the fire.
Allow the fire to burn for four or five hours, adding more hardwood to keep the fire hot. The coals from the burning logs will cover the tile. At the end of the day, heap the coals over the tiles and then ashes on top of them for cooking the tiles through the night.
Uncover the tile the following day when you no longer feel any heat rising from the top of the coal pile. Brush off the ash and use the fired tile as your replacement tile.