This pond was built in December 2007 in the earlier days of my turn-the-front-lawn-into-garden project.
The tires came from a park mowing tractor so are wider than normal tractor tires, giving extra height to the pond. You can usually pick these up free, in New Zealand anyway, from large tire repair and supply workshops: mine came from the parks maintenance company I work for - free disposal for them and free supply for me!
two tractor tires (one, two, tractor, car - your choice)
large cardboard box, old carpet, etc
thick polythene sheet from a local BORG (Big Orange Retail Giant)
flexible drainage coil (I had this lying around)
geotextile (eg weedmat, mudstop, etc) [oh, or you could use old carpet!]
soil, container mix, or compost
water plants and land plants
two terracotta pots
reciprocating saw, jigsaw, hacksaw or even a sharp sturdy knife
short length of 25mm PVC pipe