I dug a 3/4 acre pond using a bulldozer and excavator. PM me if you want to talk about it.
Basic rules of pond building:
If you have heavy clay soil, great.
If you have sandy, well drained soil, bad.
Don't make sides too steep - dangerous.
If you want fish, be aware of depth requirements.
Be aware of geology - around here, once you get down 10 feet or so, you're into shale, and you'll have a pit, not a pond, if you dig into that.
Pay someone. Make sure they are clear from day one that if the pond won't hold water, they will fix it. If you have heavy clay, it will hold water better. Otherwise, you'll need to bring soil in to line the pond. Make sure you have plenty of water, our pond has 7 small springs feeding it. Some ponds have one strong spring feeding them. If you divert stream water to the pond it will fill with silt unless it is well screened and filtered prior to entering the pond.
Ponds with liners are pools. Liner acts as a benthic barrier, and inhibits the development and growth of the more desirable types of botanical life forms, which in turn leads to higher levels of less desirable botanic life (since nature will always find a way to balance the botanical/biological balance in an aquatic environment) and you run the risk of ending up with a slimy bottom and algae blooms at the surface.