I wouldn't bother with software, just find pictures of ponds and copy the ones you think look good. Make it deep enough so you get a good amount of water in it and if you want plants in it you need to have some shallow areas for the plants.
Are you thinking of a formal or informal pond? How many fish do you want in it?
Michael, I have had some experience in this field as it is my profession. I have never used planning software as my brain does not function in this manner.
Koi are easy to keep as are goldfish. There are many ways to construct a pond and maybe you just need to research the different methods and choose what you like.
When I lived in Newcastle I used to purchase pondmaking products, fish and plants from Ledora Watergardens