The most common questions asked about koi ponds are about how big and deep the requirements would be. It is so hard to answer, since there are so many considerations needed. Instead, I would normally give a simple checklist questionnaire. How many koi fishes do you intend to keep? What is the maximum space you can provide for filtration? Are there children living with you, making a sixfoot-deep pond dangerous? Who will maintain the pond? Do you have concerns with water and electricity bills?