hiya - not sure what zone you're in but my dad lives in zone 5/6 in RI and has a koi & goldfish pond that he built about the size of a wimming pool. This is his hobby so he spends alot of time on it. Here are a few tips. Start small & experiment before pouring in alot of money. See what works & what doesn't work in your area. His fish survive the winter months of New England b/c they hibernated underneath the leaves & frozen ice on top. He lets the leaves fall into his pond in the fall & this protects the fish. Don' t worry about the food b/c it breaks down from the leaves & algae. The ice thaws in the spring and he cleans out the leaves. He also puts in water lilies in buckets with rocks to weight them down. This also helps neutralizes the water. The part that needs maintaining is a good filter. He used an old bathtub at one end of the pond that's slightly lower than the top of the pond so the water runs off into it. He put a PUV pipe to go back to a stone waterfall. There is a pump in the bathtub too. This is constantly running. Also expect to lose alot of water due to evaporation in the spring/summer/fall months and overflows from the rain & storms. Go to a fish store & ask questions & the owner may also know of people in your area who have ponds. Good luck!