A common and middle of the road sized pond is 11' x 16' that is 2' deep.

This is a great size for a novice and large enough for future desires of an experienced hobbyist.

That would mean a pond volume of about 2640 gallons. The liner size would be 18' x 23' and you would want to figure purchasing equipment, like a filter and pump for a 3000 gallon pond. If your pond will get mostly sunlight and little shade and you plan on fish, you should figure for filtering 4000 gallons.