I didn't see this until now. I've been busy with my pond, so I hope you understand.
My pond is 1500 gallons. I've lost the exact measurements, but it is 3-1/2' deep on the left side, and about 18" deep on the right side (bog area). It's approximately 12' or more across on the deep end, and 8' or 9' on the bog end. That's a very rough estimate. If you want to have Koi, or large goldfish, it really should be a minimum of 3-1/2' feet deep because this protects the fish from predators. I know some of people in our area that have ponds 2-3' deep, and they end up losing all of their fish just from birds and raccoons in our area. The bare minimum, they say, is 3-1/2' deep. They wonder why mine is so successful, and that's why. Also the large rocks provide shelter for the fish. It's amazing how many fish fit under one rock, and they must be packed in there like sardines.
You can also check out Koi-bito.com forum and see what people have built. They are very hard-core Koi experts, so watch out.
But there is some fascinating information to be had. Just a word of warning for hobbyists, they will give advice to us, but have very little tolerance for people that think Koi can live in a 100 gallon pond in the backyard, for example. I think that my size of pond is the bare minimum the members will try to help out with.
We did most of the digging for this pond, and then hired a landscaper to do the rest. It cost us $9,000 to have it built, not including plants. The landscaper gave me the goldfish - 10 of them. Some of them quite are quite fancy. He put in equipment that was good enough for a pond twice this size. In some ways that is good, and in some ways that is not. It has worked out well in the long run.
Got any more questions, just let me know. For technical advice, ask
koi-bito.com/forum, and they will answer it much better than I can.
Good luck with your pond, Michael.