I built a pond in my terraced house garden, probably a bit smaller than that in the article, but it is square and I used a pond liner. I achieved the shape by simply folding over the edges like if you were wrapping a present, only the edges are on the inside. as long as all of the the liner reaches above the water line it doesn't matter how many folds and creases you have, it all flattens out when you put the water in, you can hardly make them out now the pond is fully established. I used sharp sand to ensure the liner doesn't get punctured, make the sand a little wet so you can paste it to the sides of where your pond liner will go. I also suggest you put a couple of shelves in, 5-7 inches deep for border plants and 2-4 inches deep for birds to bathe and drink from.
Our pond is now 3 years old, and although we have koi and gold fish, there are also a large number of invertabrates living in the water, sheltering between the plants.
We have included a water fall in the pond, and the lillies dont seem to mind, but no fountain, I think that detracts from the natural look.