I usually begin to prepare the clay for handbuilding the day before I make the cups. I like to cut a 25-lb bag of clay into three thick slabs, and dry those slabs in the open air until they are quite stiff but still just flexible. Then, I wrap the partially dried slabs tightly in plastic and set them aside until I need them.
Clay for cups should be about 3/16 inch thick. Set your slab roller to than thickness, or roll the slab as evening as possibly to that thickness if you do not have a slab roller available. The stiff slab that was prepared with soften up when rolled out, and should be just right to take impressions from texture tools. Ideally, it should be moist enough to readily join to itself, but dry enough to stand up into a cylindrical shape after cutting to measure.