What would I need to build a basic container pond for Texas weather that could house a few common goldfish ponds

Im considering setting up a basic above-ground container pond with some plants, maybe have a gravel/sand substrate. Im curious what container I would need to buy to comfortably grow a few common goldfish to full size. Im also curious how filtering and what-not is supposed to work for a pond like this that would be outside, since Im only used to indoor aquariums. I know how to properly care for an aquarium, and need to know how similar or different a pond is.

How many gallons do you think the tank held? Also how did you go about adding new water (water house? lots of water conditioner?)