Although commercial aquaculture tanks are usually made of fiberglass and other materials, the prices are usually out of the range of the small scale DIYer, and that includes myself. Sometimes the shipping is nearly as much as the tank!
I prefer plastic stock tanks that I can get either from a farm supply or other big box store, or fortunately for me, I have a plastic tank manufacturer within a reasonable driving distance that sells me tanks that have minor flaws for about $100.00 for a 4 to 6 foot diameter circular tank. I prefer circular tanks for properties that will be covered later.
Here is a 7-8 foot plastic stock tank I use for my summer outside system and a holding tank, when seining the big trophy pond. Will not fit through a normal doorway!
Here is one of the plastic tanks I purchased off of the plastic tank manufacturer. They are actually initially much taller but they will cut them down to whatever height I prefer.
Do not use a galvanized stock tank for fish like this one unless you coat it with a fish safe pant like the one below.
Even then, you are better off getting a plastic tank that will probably be cheaper than buying and then painting a galvanized tank, (The paint isn't cheap). At some point the paint will peel up somewhere in the tank. When it does that, it's only a matter of time before water works it's way under the paint and the paint and tank progressively deteriorates. I was given two galvanized tanks and have since given them away.
Intex swimming pools like the one below, that range from 10 feet to 24 feet diameter are another option. Very cheap! A 10 foot pool can be just over $100.00 including free shipping. Many times local big box stores like Walmart, K-mart or Sears even carry them.
You can either raise them on 6 by 6 posts lying on the ground or floor with plywood as a base to elevate the tank to install a center drain, or you can trench in a drain in the ground and install a drain through the bottom of the pool similar to a liner which folks do routinely with koi pond. The remainder of the trench can be filled in with soil or sealed with concrete.
Too be safe for fish use you should wash down the insides of an Intex pool with a dish detergent soap solution, and then rinse. Then fill with water and let stand a few days and rinse again. There may be plasticizers present that could be harmful to the fish.
I know shrimp growers that have used these for years with no issues indoors.