To create a stone mantel with a pattern, begin with uniform stone tiles. By taking a class in stone etching, you can learn how to use stoneworking tools to create your pattern, such as a stenciled pattern, on stone tiles. Affix stone tiles in an alternating pattern onto a stone or brick mantel piece. The resulting design with hand etchings is your handiwork.
A larger project involves learning how to cast stone. You can mix your own mixture of stone, concrete and/or cement materials, and pour it into a mold. Another option is to purchase an entire DIY kit to create a stone mantel, potentially saving you the thousands of dollars you would pay a stone-casting contractor. This type of kit contains all of the materials and tools you need to create stone veneers. You could also purchase just a concrete mold and create your own stone veneers. You can buy a mold small enough, for example, to create large rectangular veneer pieces. Combine these rectangles to form the mantel shelf.
You can buy stone bricks for the fireplace frame just as you would if you were building a retaining wall in your garden or along the foundation of your home. On the top of the fireplace frame, create your own stone pattern by using mortar to bind stone pieces to the bricks. These stones must be flat and smooth on one side so the mortar is easy to apply. Your resulting stone mantel looks slightly irregular just like the stone bricks around the fireplace. To create a contrast, use stone fragments of a different color than your stone bricks. To make the overlay fancier, apply a glaze on the stone pattern. If you don't like the natural tone of the mortar, use a different color glaze to create a contrast with the stone glaze.