To sculpt stonework, these tools will assist you. If you already have sculpting tools, that's even better! I will get sculpting tools next time I'm at craft store. For now, this is my 'make shift' kit. Tools you may need are: toothbrush or stiff bristled stencil brush, manicure stick, small paint brush, water and tacky glue.
Keep doing small sections at a time. Take your time. You are not only a mason but a sculptor. I went back and brushed on a super light brushing of water to smooth out the mortar in between the stones. I used the rounded end of my smallest paint brush to smooth out in between the stones. A ball head sculpting tool would work better though. While the clay is moist from the light brushing of water, I then stippled the stones with the toothbrush for a bit of Stoney texture.
This is all I used to create the stonework. If I don't like the stonework when I am finished, I just won't use it. The stonework is optional for this project. So I'm pretending the stonework is my practice piece. You can do the same. Relax and take your time. Play dough is supposed to be fun. Lol Have a wonderful day! ; D