Here is a good article in mother earth news on pond building .
Somewhere I have a us gov link on getting some help in building one , too.
If I find it I will come back and update!
I have one of the preformed ponds in my yard. It is used as a small water garden near my back door. Lots of frogs live there.
I have a second larger pond made from the sheeting that was hand dug and laid out. It is filled with koi and lots of various plants. We have found newts, salamanders...