With all the materials available today, you can design; plan and build a Koi pond to your liking but keeping in mind that you need to accommodate these fish correctly.
To accommodate Koi correctly you need to remember that the amount of water surface is just as important as the depth. Koi can grow over 60cm in length, so if you are serious about being a Koi keeper then a bear minimum depth of 1.5m should be obtained. Then at least 3.5m x 3.5m in length and width should also be obtained.
Where all ponds are designed with shelves and a deep middle to the pond, you should construct your Koi pond with steep sides, not sloping sides, with the pond running from a shallow end down to a deep end. An old swimming pool might just do the trick (not that we all have one of them lying around).
You may also want to incorporate a drainage system or two depending on the size of your pond, this is easier than trying to pump the water out when doing water changes. Who really wants to jump into a pond 1.5m deep to clean it. I don't have legs that long and if I did I am sure they do not sell waders that big.
As Koi pond designs have to be large, most are built in concrete, double brick or with blocks, but I would suggest to use a liner as well for extra waterproofing.
You will need to dig down as well as building above ground, because a 1.5m high wall is not very attractive.
With having an above ground Koi pond you will also keep out a lot of your Koi predators like herons.
If you have the space in your garden to create a Koi pond then it will be one of the most beautiful water features you can ever create. Also keep in mind that where these ponds are large, which means so will be the cost of constructing it.
The larger the pond the better
1.5m minimum depth
3.5m x 3.5m minimum in length and width
The best filtration system you can afford
UV clarifier system if possible
Return from Koi Pond Designs to Koi Ponds