I've done 2 wholecloth quilts. In both cases, I designed them myself and traced the pattern onto the fabric using chalk pencils and a light box. Then I made a "template" out of bridal netting, using a sharpie to put the design on the netting - once the sharpie marking is dry, you can position the netting over the top and trace through it. That way I could refresh any lines that rubbed off.
You can buy stencils and trace those - probably a whole lot easier. And our Holice has some sensational whole cloth designs that are prestamped onto muslin.
Good luck!
Janet