I use a heavy weight paper with a center line drawn down the middle. I free hand draw on one side of the line on the paper of the form. I have drawn horizonal lines about every two inches up the length of the paper, so I then can take a measure on each horizonal line and mirror the image on the other side, then free hand the rest of the image. I use scissors to cut it out at that point and lay it on the slab of clay. The number of cutouts depends on the form image you want, for this I want two of the cutout slabs and I will use just made slabs of clay to tie the edges of the form.
Sorry, the photos are in reverse sequence. the bottom photo is #1. The middle photo is #2 and it shows the textured surface of the clay before I assemble, then I let the slabs then stiffen overnight. I like them to be able to stand on their edge and not collapse, usually leather hard.
The top photo (#3) shows a slab of clay. It can be any length or width. The slab I have made is about 5-6" wide and about3/4 of the height of the form. I score all the edges of the form and the area of the second slab (the base) where the form will attach.
I am having to publish this in parts, so that I want have too many photos up at one time, so this is continued in p. 2.