Michel J. Anders shares a small Blender on his site, Small Blender Things. The Drystone Addon for Blender allows you to create irregular stone wall patterns, that was ultimately inspired but the walls of the castles at Conwy and Beaumaris.
The Drystone Addon for Blender can easily create those irregular stone walls. In essence, it is similar to the popular Blender Addon masonry, the difference is that Drystone can create irregular patterns based on bMesh.
The Mesh that Drystone creates consists of separate n-gons and the depth is provided by a solidify modifier topped by a bevel modifier. Currently you will have to do the uv-unwrapping yourself.