Hi I've built 3 ponds in the past each one bigger than the last. Its not something that should be rushed into. It can take a lot of effort to do the whole project. My last build (see link at the end) took 5 days working flat out but there was already a smaller pond there so that took a lot of the hard work out of it.
Things to think about though.
What are you going to do with the earth you dig up.. There will be a LOT of it. I raised a whole corner of my garden with it!
I'd highly recommend a filter.. Especially if you want to see your fish
Which means a pump as well and some means of getting the filter water back into the pond (waterfall) This will need to be bought and incorporated into the design as early as possible.
Make it at the very least 2 foot deep 3 foot would be better.
The electronics are straightforward enough. Make sure you get armoured cable and dig it deep into the ground run it of an trip RCD.
I've used butyll rubber twice and a preformed liner once. I'd stick with butyll. Its cheap extremely strong and easy to work with. Spend a lot of time ensuring that your levels are right. You don't want all your water running to one end of the pond exposing the liner at the other.
If you have any questions then let me know I'll try my best to help you out.
My latest pond =
http/img178.imageshack.us/img178/593/dscn0487go6.jpg
You can see the raised area at the top of the garden from the dirt taken from the pond. The waterfall looks a bit ropey in the pic but the plants will soon cover it up and make it look more natural.
I have step by step pictures of this which I'll post in a new topic. It shows the whole project from begining to end
Scrof