I think it was my on-line friend Karl O in Pennsylvania who first suggested this, but I like to use roofing felt, aka tar paper, as a templating material. It is more rigid and durable than paper, which is handy when doing capstones like this, with an overhang. Paper would droop and tear and we’d never be sure if the final fit would be on target or not. Even with the felt, we have adjustments to make once we get the stone in place; the actual fit is never the same as the template fit. But the more accurate the pattern, the more efficient the installation will be.
These images were taken at the Beast Wall project. This sitting wall frames a new patio we just recently built there.