The size of the pond will influence several decisions.
Generally, extremely large ponds like those found on farms or
larger estates will be earthen ponds while small, deck ponds
will be made from barrels or plastic containers. Remember that
the larger the pond, the better it will buffer against rapid
changes in water temperature, pH and other chemical reactions.
Most typical backyard ponds are in the 500 to 2,000 gallon
volume range.
For more detail on
each type: