You can certainly put a pond there but that isn't very big for Koi and you will have critters visit even that close to your house. You could certainly have a nice goldfish pond of that size.

My calculations, assuming your pond will have straight sides with no shelves, are coming up with approximately 800-900 gallons. I don't think you'll be able to find a preform that goes 3' deep, or at least I've never seen them that deep. And if you did, it would likely have shelves around the edge. Just remember that shelves will reduce the total gallons significantly. Measurements are calculated from edge to edge, with sides going straight down.

If you're handy at building, you might consider building a wooden frame with good reinforcements and putting in a liner. If you do that, be sure to add some water in the bottom (to settle the corners and edges) before you secure the liner along the top edge. I've seen people make this type of a pond for a QT or a winter holding tank, but water is very heavy so you'll need to really make sure the sides and corners and edges are well secured.

At 800 or 900 gallons, adhering to the 250 - 300 gallon average per koi, you could get away with 2 or 3 koi if that's what you want, but I wouldn't put any more than that, since they won't have much swimming space.

If you include shelves, you would probably have a pond with about 500 to 600 gallons, max, which as has been said, would certainly make a nice goldfish pond.

I would worry about the strength of the concrete that will be supporting the pond. Do you know how thick it is? Does it have any rebar? The contractor who installed it would be able to tell you what weight it can handle. It would be horrible to damage a patio like you describe.

If there is a problem, you might consider a pond on the outside edge of the actual concrete. That way you wouldn't need to worry about damage and it could be added in to the screened area with little difficulty. The depth could be whatever you wanted. You could even use a large stock tank and sink it partially into the ground and have a seating area built around the edges.

I've talked to our homebuilder and he assures me the size of pond I would be talking about would hold the load.
I would LOVE to have the pond in the backyard, but we already have water snakes close to the house due to the lake being so close to us.
The screened in porch is really the only option I see available to me.
A question would be, if Koi need 3 foot minimum, why do I see ponds in retail that a more shallow, with large Koi, 1 foot to 1 and 1/2 feet long outside. (Alabama was the state). I live in Texas, and haven't been able to visit any retail here yet.
@sleeplessinftwayne, how are you saying I could put the stock tank in ground added into screened area with little difficulty? Are you talking locating pond in ground THEN adding more screening?

You see shallow preforms with koi for a couple of reasons. Either the owners are just unaware of how unsuitable the shallow preforms are for koi or the set up is for display rather than for long-term. If the retailer can get you to buy it, they may not really care if it is an appropriate set-up. Koi grow and they need to be able to dive to truly exercise. An 18" koi can't dive in a 20" deep pond. And 18" is a very conservative size for koi....

Be sure to check with your insurer to be certain they will cover liability, then go as deep as you can. Maybe have a raised seating area around it for viewing? Another option would be to get some fancier goldfish that are not as finicky about water quality and do not need the depth as much as koi. Wakin and watonai have lovely fins, and there are some gorgeous shubunkin. Also, Oranda might do really well in this type of setting.

Fritzi, that was the general idea. Extending the screen around the pond seems to be the most reasonable way to go. A three foot deep pond sitting on top of the ground or cement is not going to be easy to look into. At most a pond that is 18 inches above ground or possibly 2 feet if you are seated fairly close will give you good viewing.Any higher and your view would be curtailed.But a pond that shallow raises problems if you want Koi. An article I read that made the 3 ft. minimum depth a rational decision discussed the need of such a potentially large fish for exercise. By restricting the depth the fish can dive at speed, you limit it's muscle development. I wish I had the article at hand but that was several years past and I don't remember what the publication was. Jennie must have read the same article(s). Her opinion on the retailer with the Koi in shallow pond is one I can agree with.

The only pond builder of any stature near us has his display pond inside a greenhouse type retail building and it cannot be inground. The pond stands almost four feet high and has sides of stone for terracing. The falls are 6.5 feet above ground. The Koi love it and he often boards fish and plants over the winter. But you have to be right up against it to see the fish. At five feet tall, I have to lean right up against it to see all the way down. It needs a double bottom drain to reduce cleaning because it is so difficult to use a pond vac without a platform of some sort.

That is why I think it is more reasonable to put the pond partly inground, off the side of your patio. Extending the screen around it to keep out the snakes seems the most pleasing and efficient solution unless you want to go with another type of fish.

Would like to encourage you to consider a goldfish pond. These are now being bred for ponds - with bright colors and patterns. Some comets are very koi like in appearance with with similar body shape and long flowing fins. Shubunkins with wild metallic blue and red coloring are another type. The difference is they only grow 10-12 inches as opposed to the 3-4 feet that a healthy koi can reach. A 24-36 inch depth is perfect for goldies. If I was building an above ground pond I think I'd want it a little lower - say 24-30 inches - to make it easier to view.

Yes Ive seen large koi in shallow conditions and it was not pleasant. The poor things basically looked like sardines in a tin - could hardly turn around. In comparison, a school of koi swimming across a large pond, large enough to hold them (say 4 or 5 feet deep, 15 feet w x 60 feet long), is a really majestic sight, the way they all swim in unison. You just don't get that effect when they're too cramped.

Since the whole point of a pond is to get joy and feel happy from looking at it - trust me, you want to have healthy happy fish!