I don’t have a slab roller either (been looking for a used one). I find the slabs rolled with a slab roller have less warping though. I put a garbage bag over a large board, roll a slab at the college and lay one slab on top, then a sheet of plastic and another slab and so on. I take the slabs back to my studio to work on them. Be careful not to pile up too many slabs otherwise they will be too heavy to lift (I’ve done that). I can store the slabs under plastic for several days before they get too hard to work. Pastry rolling pins come in a large size 18 inch, I think - how large a slab are you needing?

By the way what type of rolling pin do you use? I am thinking of getting a silicon or aluminum one since the clay sticks to the wood one I use.