Hi Khris and Richard, I would be happy to share my approach.
I had previously made some simple, small, rectangular stamps out of brass. The picture shows two of them. The crude handles are made from Milliput which does the job. The cork is mainly used to protect the end of scapels and I used it to allow me to position the end of the stamp for the photo, not because I have been drinking bubbly. At least not today.


A spare piece of hard, thin plastic was cut to shape and was covered with a thin smear of Weldbond. I sure any decent wood glue would do. I use Weldbond as I am familiar with its properties. A thin layer of DAS modelling clay was pressed flat to the required thickness. The glue bonds the DAS to the plastic base. While the clay was still damp I pressed each sett or cobblestone using the brass stamp, one at a time. I wanted to have a look that was not strictly regular and doing it by hand achieves that I think. It doesn't take all that long and mistakes can be rectified easily enough before the DAS dries. Once dry I gave it a ink wash and when that was dry used Winton oil paints to shade it. When the oil paint was fully dry I used Mig weathering powders, mainly towards some of the edges.
I hope that explains my method reasonably well. If not I would be happy to clarify.
PS. I would welcome any constructive criticism. I can see from the photos I need to work on the stone walls a bit more.
Cheers
Snowy