Here is some pics of my
koi pond build right now. Obviously way more then you want to do, but Ive been building ponds for years. 2' is absolute bare minimum for any type of fish not only because of winter freezing but predators and also with such a shallow pond water temps can change drastically from daytime to night time. Check out
www.koiphen.com lots of great info on there. As for your pond let me know your desires for the pond and we can take it from there. You can go all out with bottom drains(required in my opinion for any pond), all sorts of returns, monster filtration etc or you can just to a plastic 80gallon pond with
submersible pump, barrel filter and a uv. last pic you can really get an idea of how deep my koi pond is

