split peas or lentils work great. Glue them to your surface then fill them with spackle leaving enough exposed to represent your cobblestones.
Cork, like you would get from a craft store or DIY pale, cut and glued.
lay down a layer of plaster and scribe your pattern.
Doll house supply places make a great cobblestone pattern that is a thick latex. It can be cut to shape and painted.
Several companies make sections of cobblestones, with different surfaces and patterns, from resin and plaster.
Mike
"Imagination is the dye that colors our lives"
Marcus Aurellius
A good friend will come and bail you out of jail...but, a true friend will be sitting next to you saying, "Damn...that was fun!"