1 - Kiddie Pool - use a sharp knife to cut it down so it'll hold liquid but isn't a big trip hazard.
2 - If you have a solid floor, you can get outdoor pond liner, which is a very heavy mil plastic, used for building ponds in dug out holes. Build a frame of 2x4s around your brewery, don't bother with a floor / bottom. Lay the plastic in it, throw a few staples in around the perimeter to hold it, and tape over them wtih the special tape they sell for this material. Now you can build your setup any size you want.