My advice is to find a good Koi keeping forum, and research proper pond construction.
The ponds i built when i used to landscape full time in college were improperly built, i was just doing what the owner told me, they just ended up being a nasty hole in the earth. When i decided to build my own pond i started research on Gardenweb, and built it the best i could. It turned out great for Goldfish and my dogs. It was about 12' long by 5' wide and 2' deep at the deepest. I lined it with flags stone that i glued in place with
http://www.coastalpond.com/e6000-black- ... -4993.html . I had access to free flagstone and free e-6000, otherwise i wouldn't have done it. I made a homemade filter out of a plastic storage bin and a ton of scrubbies, and used a pond pump. It is much like a large fishtank.
The first thing i would do is decide on a dimension for your pond, width, length and depth. For a proper pond it will need to be deeper than you think, research that. You will not want to fill it up with stone as i mentioned before. You'll want a bottom drain, filter (or two, like a pool) and a pump. I'd figure out a budget, and then see what can be done with that.
As far as design, i always liked the ones that look sunken into the ground like a natural setting. Too many people pile rocks all around them and it's just a dead giveaway that its man made. Of course you want it set up so that surround run-off does not get into the pond. But you can accomplish both the sunken look and no runoff. If it were built into a flat yard, i would want the stones that go around the pond, and on top of the liner's edge to be level with the ground. Meaning that the tops of those stones would be like maybe an inch above the ground. Just to give you and idea of what i mean by "sunken".
While you are at it, it's always nice to have a little stream flowing into the pond but not necessary.
Yes please take and post some pics, and if you do find a forum that you start posting on about your project either link it here or keep posting here too, sound fun and DD will really enjoy it.