Proposed garden pond

Hi Maj, well, firstly you can go onto a site where they sell pond liner, such as Bradshaws and you will find a pond liner calculator there for you. It's basically length X width X Depth I would include an extra 12" all round for the overlay on the banks. Don't forget to calculate for some extra for the channel of the stream.

Well, my Wild Life pond is just over 3' in depth but anything from around 2' should be fine. I have 3' depth to ensure that any pond life is protected at that depth from freezing although I also stick a floating heater in if there's a case of a cold snap.

Another point, you might find as the pond matures you might have to go for a paddle or wade as I have to in order to tidy up from dead/dying vegation on the banks from the water.
If you do always wear footwear of some sort and make sure you have no cuts or abrasions on your feet. I failed to do either some years back and had a tiny cut on one of my feet and the result of that was a swollen, infected foot that had me in agony. I ended up having to have antibiotics to cure the infections, so now I use Chest Waders to paddle around when cleaning up the pond.