Here's the toot on how to make cobblestone roads
Apply a layer of plaster of Paris to the road surface, let it dry and sand it down to the profile of the road. (This will give the shape of the camber as well as something for the next coat to key to).
Next, get an open mesh washing bag, (available from supermarkets... the type you put your loose articles in, to throw in the washing machine).
Or for a square/ less regimented cobble, you can use garden wind-break material.
Cut it into a strip of the required size... slightly larger than the area you wish to cover, (Make sure it has no creases in it)
Now the fun bit.
Apply a thin layer of plaster over the road surface.
Lay the material over it.
Then apply second coat of plaster over the material.
Squeegee it down with a plastic applicator. (Very much like screen printing).
Go right to the road edges, and scrape it down so the top of the material is exposed. (Make sure you have squeezed it through properly... otherwise the cobbles may lift with the material.)
Very carefully peel back the material as soon as the plaster starts to go off (while it is in a turgid state), this will give a slightly broken effect to the edges of the cobbles.
And there you have your cobblestone road.
Once the plaster is fully set, paint it, and seal it with a few coats of future. (Next steps not pictured). Give it a nice muddy sludge wash, then sprinkle and brush it with rubble dust, then seal it all up with dull cote.
It's quite a simple technique once you get the hang of it.
The material is available in different grades, keep an eye out for it, for different sized cobbles.