Well you can buy any of the commercial ones, the CMON store stocks quite a few. In addition to the big range from Dragon Forge, Enigma do a couple too:
http://www.coolminiornot.com/store/section.php?xSec=60
Other than just buying, there are two basic options in making something like this: building (assembly) and sculpting.
If you want to make it up from pieces you can use cut plastic card, lead foil, paper or card, rolled-out putty. Paper and card card can be sealed with varnish, PVA glue, shellac or even wall paint to help it not swell up too much when you paint on it.
For any of the smoother materials if you want to add some texture other than impressing them with something you can stipple with stiff paint to get quite a convincing stone-like texture, particularly if play with it a bit and vary from block to block. It\'s often best to texture, then cut up and glue down rather than try to texture when they\'re in place.
You might need to then add something to simulate the grout/mortar in the gaps.
If you want to sculpt this, it\'s just a very simple method of mixing the putty, smooshing in into the recess in the base and flatten it off, then add the grooves. It\'s a bit more complex than that in practice in that it\'s best to wait for the putty to cure to certain stages before you add some detail but in essence that\'s it. This can often be the slowest of the methods though, since you can fiddle with the divisions between stones and the texture for quite a while to achieve a believable pattern and to get them to look right. But the results can be worth the time; textured putty gives one of the best effects, since the texture is into the surface, not on top of like with paper, plastic or foil. You can use small stones to gently press in some basic irregularity, stiff bristle brushes or a new toothbrush to add different kinds of very believable texture.
Another advantage with the putty method is you can gently impress the mini into the putty (just slightly, you don\'t want it to look like the feet have sunk into the stone) to give a better footing. This is good for any mini that has irregular feet that don\'t sit dead flat.
Man, who\'d a thought you could write a whole chapter on just this?!
Einion