We put one in a couple of years back. Couple of thoughts: assuming you plan to get fish. you'll probably need a pump and filter. Before you start work out where the pipes and filter box are going to go - and (something I missed) whether you can arrange a soakaway strategical placed so you can undo the big plug under the filter. box so the sludge drains away. Remember the pond itself needs an overflow and soakaway too (I did remember this luckily, as my garden guy had forgotten). If you have different levels in the pond I suggest the depths are flat rather than continuous - this means your plants won't fall over. Another hint is to get the nylon bag plant "pots" rather than plastic pots as they are mire stable. Electrics for the pond are I understand "notifyable" (if that's the word) so you are not supposed to diy and are meant to get a sparky. Ideally get 3 or 4 sockets; pump, UV lamp (part of filter) plus provision for separate fountain and lights . I went for koi carp and luckily only got small ones initially (less than a fiver each I think). A year on they are 10"+ so it wasn't worth paying £50 or £100 for big ones. You want the plants, pump and filter all working for a while before you risk getting fish. Another minor hint is that the pipe for pump isn't very bendy so get some plastic 90 degree bends rather than try and bend the pipe itself. Also our filter has 75mm return pipe - but the ones from "pondkeeper" were some quite sophisticated push fit ones from Germany and very pricey. After a lot of searching on the internet I did find cheap pvc drainpipe in 75mm but you can't get it in wickes. Another thought - we don't have a heron problem here (so far) but it's something to be seriously concerned about. Apparently seagulls (we have lots) drive them off - dunno if that's true
Our pond is under a tree - not recommended as it fills with leaves which MUST be fished out daily in the autumn else the water goes manky. You do need to do something on the pond nearly every day - nothing onerous but keep on top of it. Fish need feeding ideally a couple of times a day (but not at all in the winter) slime needs pulling out and the filter needs cleaning out weekly (or more in summer) . I don't mind doing this.
I've got on well buying stuff from pondkeeper.co.uk and found them very helpful on the phone explaining stuff (eg filters). They were recommended by my garden guy initially, and I've got all the kit side of things from them - plants and fish locally.
By way of history, in a previous place there was a pond there when we bought it and my first though was "stinky old thing, we'll fill that in" but I really got to like it. It was goldfish and frogs there rather than koi.
I'll add more pics and thoughts later.
I love my pond and will almost certainly have another at our next place
