Hello from a fellow U.K. ponder, we seem to be netting a few more these days! Hope to see you around
Agree with what's been said above....plus you are not then restricted to what size/shape is available, you make it your own. Your back and your wallet dictate a lot. Remember most fishy ponds need filters/pumps etc, all based on water volume/fish population, it can all add a lot of £££'s. Please do ask as you go along the process of whatever you decide to do....and show pics regularly, not after it's all filled with water! We may have suggestions that could improve your design, especially if you're not familiar with pond construction. Give us as much info as poss......where if will be situated, full sun ,shade, overhanging trees, fish or fish less, depth, width, length, type of fish, the list is endless! You can never give too much info....and we often beg for more!