I also built a 650 gallon water storage tank. It has a steel and wooden frame, with a pond liner in it. I could have put in tanks, but I can get more storage per square foot. Plus I turned it into a small water garden and put a couple of fish in there.
Here are Bob and George in their new home. They are about 9" long. Their old home was a 10 gallon tank! Sadly, George went to fishy heaven a few months later.
I put in a bench on the south side which is built out of some scrap plywood. I also made some planters out of some cedar and put casters on the bottom. It allows me to roll them under the benches to get them out of the way.
Here are some peppers, broccoli, and