What's your budget? How handy are you? Surface Size?
Don't go to small!!!! BIGGER IS BETTER!!
I started a pond/patio project this Spring. It was the final justification to the wife for a tractor
Mine is coming along slowly, but I am making progress now that digging is done. It will be roughly 5' diameter and 2' deep so 300gals of water with a waterfall 3-4' high set into the hillside. I started out with a 150gal and after I was half finished it looked really small so I started over again. We're going with a 15'x30' stained and stamped concrete patio in coloring similar to the retaining wall.
http://www.johnpinnell.com/gallery/main.php?g2_itemId=727
I was shocked when I started pricing liners, pumps, filters, skimmer, etc. Seems like every item is $100+ and it all adds up. At the minimum you'll need a liner, pump, and a filter. A skimmer would be a good idea too. you'll be in it for $500-$1000 if it's to be big enough for the dogs taking a dip.
Liner - I went with a RubberMaid 300gal stock tank ($190) that will be sank in the ground almost completely. The rock wall will ring the pond and overhang the edge to hide the stock tank. We have lots of animals around, neighborhood dogs, etc. I wanted a rigid liner with our rocky soil and the risk of puncture if an animal fell in. When/if it does leak years down the road it won't be difficult to add a plastic liner later.
Filter/Skimmer - $150-250ea (making both on my own for $50ea) you'll want something to keep the water clear. I suggest a biofilter of some sort, but that requires a continous running pump. You can make one of these yourself. Read up here:
http://www.skippysstuff.com/biofiltr.htm and it's easy to scale up or down in size.
Pump - $100 - unless it's just going to be a water feature with plants only you'll need a pump to aerate things for the fish. An important thing to look at is power requirements. The new mag drive pumps run on mere watts and are worth the extra initial cost as they will use less power. You'll need to calculate your flow needs, head, etc to get the right size. Ideally you want the pond volume to circulate completely in 2-3hrs so base your pump from that.
Plants - you'll want some lilies and anachris for oxygen and nitrate removal, especially with your plan for fish. Some plants are submerged and others need to be near the surface. That's why you see the preformed ponds with 2 different levels. Since mine is 1 level I'll place some structure in the pond for fish cover and setting surface plants on.
Electric - you'll need it for pump and probably lights to. I plan to run a seperate cicuit and put it on a 20A GFCI Breaker. Plan for your conduit run before you start laying the design out.
Alternative Materials - Keep an eye out for things that will work with modification. I'm making my own skimmer and filter using a couple of PVC Shower Drains and a large square buckets for $50 in materials as opposed to $250. If you aren't having fish then I've heard rubber roofing material is cheaper than a true pond liner, but you may need to run it through a season or 2 and change the water out several times before adding fish.
Landscaping - I'm getting rock from the local quarry for $15 all you can load by hand (need 7-8loads for the wall) on Sat mornings. You'll need a load of sand for putting under the liner to level things out. Having things level is very important. Whats around the pond is more important than the water itself. If it doesn't "look" right it'll just be a whole in the yard.
Water Levels - If you plan on a waterfall you'll need a liner under that too. Otherwise you'll quickly pump the pond dry. Also allow for wind if you're using a fountain. A torrential downpour could cause an overflow so you need a plan for diverting surface run off away from the pond.
I'll know more when mine is finished this fall.
