Since the introduction of fish friendly flexible pond liners like EPDM, constructing your pond has become a do-it-yourself project that can be accomplished over even a single weekend. We are going to discuss this type of installation. You might also consider a pre-formed pond, a concrete pond or an above ground pond. After you have determined the size, you will need to purchase the liner material. Measuring for a liner is not complicated. You can purchase it in pre cut standard sizes or have it cut from a bulk roll. It is usually sold in 5' increments so that if you need a 16' x 19' liner, you would purchase a 20' x 20' piece. You need to measure the width plus twice the depth and then the length plus twice the depth. Always allow at least a foot or two for overlap. You should also plan on an underlayment. This can be as simple as old carpet padding or a non woven fabric that is made for this purpose. It will provide additional tear and puncture protection for your liner plus it helps in soil stability and erosion.