but I did more than what I would have gotten from hiring. I usually find doing it myself cost the same as the quote. I start off planning on saving money by doing it myself, then I get involved and start having fun and go overboard with ideas and wishes. It costs the same, but I like the end result better because of the details.
No kidding???????

Our pond took on a life of its own after it got started. Wife thought the shore line looked too plain, wanted some "character". So added three curves/coves that were not in the original plan. Fish structure? Don't get me started. Nice place to walk would be nice so don't get feet wet or make 4 wheeler tracks. Tons and tons of rock. Don't want an eroded shoreline. More tons of rock. And the list goes on. No friggin way could I have planned out what we ended up with or afforded to pay a contractor (ok, ok, I probably spent nearly as much money in the end, but when it goes out more metered we don't have to admit how much it really cost and get the shock of a single big check to write. Let's just say my Diesel bill and lime bill was "up" a little for the year. I actually have no clue what it cost me and don't plan on figuring it out. The bills are still getting paid, and that is what is important).
I would say if a person wants to "do it yourself" DIY project, the very last good reason is to save money. For me it was the learning process that I always enjoy. After driving a tractor round and round for 40 years it finally got old, even though it has been what I loved and knew I wanted to do since 5th grade. The pond gave me something new to learn. To experiment with. Same with the fish. It is the learning process, not the fishing that holds most of my interest. Maybe in a couple years will need to have a PBF get together so I can get rid of some of the things.

I would whole heartedly agree fish n chips, that what I ended up with was vastly better than if wife and I had sat down, made a plan we could stick with, and told a contractor to do it. My pond would not be nearly as nice as it is because the dream expanded as it went along.
So if the last reason to DIY is to save money, I would say the best reason is if you like learning, if it does not bother you making some mistakes, if you will not loose a lot of sleep over those mistakes, and if when things turn out to be a way more work than you expected you buck up to the challenge and enjoy it instead of wishing you never started.
That would be the only way I could ever suggest someone build a pond themselves. They also need to be able to accurately evaluate their own learning ability and skills level. Some people........... make that a LOT of people, should never attempt it. But farming and operating equipment for most of a persons life is a good set of skills to start out with.
Do it because you want to do it, not to save money.