Let's hope
T
TLkmDN
chimes in here, he's pretty experienced with this 
I'm wondering how you would go about building a large concrete pond, like the one TLkmDN's got. My understanding is this:
You want to first (obviously) dig the hole wherever you want the pond, whatever shape it's going to be. You'll then put chicken wire and/or rebar down, then get the concrete poured on and let that set, and you've got the basic frame of the pond. OR, you could use cinder blocks to fill in the frame and then cement over them. After that, you can put a liner (like linoleum tiles) down and/or paint it with Pond Shield or a similar epoxy paint. After that you've got a pretty basic pond form.
After that you've gotta get filtration worked out. I guess before you put everything up, you want to plumb in grated drains to lead into either the floor or side walls. Where can I find a plumbing schematic for a pond like this? After that it will go into a sump, which will be a big long deep tub built the same way as the pond's frame, and you add in baffles too. After that you want a few big submersible pumps to pump the water back through returns in the walls of the pond.
For media in the sump, would you go with something like filter pads and sponges first, then a baffle, then some more filter pads and large bags of bio-media, then even more bio-media, and then a return section, also including a couple of huge UV sterilizers?
Also, how would you heat a large pond like this (something a little under 20,000 gallons)? Can you over filter a pond? Should there be surface skimmers? What kind of turnover would you want?
Thank you!

I'm wondering how you would go about building a large concrete pond, like the one TLkmDN's got. My understanding is this:
You want to first (obviously) dig the hole wherever you want the pond, whatever shape it's going to be. You'll then put chicken wire and/or rebar down, then get the concrete poured on and let that set, and you've got the basic frame of the pond. OR, you could use cinder blocks to fill in the frame and then cement over them. After that, you can put a liner (like linoleum tiles) down and/or paint it with Pond Shield or a similar epoxy paint. After that you've got a pretty basic pond form.
After that you've gotta get filtration worked out. I guess before you put everything up, you want to plumb in grated drains to lead into either the floor or side walls. Where can I find a plumbing schematic for a pond like this? After that it will go into a sump, which will be a big long deep tub built the same way as the pond's frame, and you add in baffles too. After that you want a few big submersible pumps to pump the water back through returns in the walls of the pond.
For media in the sump, would you go with something like filter pads and sponges first, then a baffle, then some more filter pads and large bags of bio-media, then even more bio-media, and then a return section, also including a couple of huge UV sterilizers?
Also, how would you heat a large pond like this (something a little under 20,000 gallons)? Can you over filter a pond? Should there be surface skimmers? What kind of turnover would you want?
Thank you!