There are two ways to create a countertop using concrete; the first is to pour the concrete directly on top of the cabinets and then hand trowel the surface. The second is to build moulds for the countertops and pour the countertop offsite.
Making the template
If using the pouring method you need to create a template for which you trace the countertop base on an oversized piece of wood veneer or connect strips of wood veneer. The template should be the exact size of the countertop base and not the size of the countertop that will go on it.