In this article the pond size that will be used will be:

15ft x 10ft x 3ft deep
approx 12000L (2700 UK gallons)

Pond liner
Firstly find out the maximum dimensions (deepest point, widest and longest points) of the pond:

i.e 15 foot long x 10 foot wide x 3 foot deep

The calculations
length + twice the depth + 2ft
width + twice the depth + 2ft

This gives you the size of liner in feet, the extra 2 foot is so you have a 1ft flap all the way round to tuck under flag stones or build soil or something under and then fix it down over the soil so you have a rim and to stop the pond collapsing in on it's self.

i.e
15ft + (2x3) + 2 = 23ft
10ft + (2x3) + 2 = 18ft

Liner size = 23ft x 18ft

Pumps, filter boxes and UV lighting
The pond pump running the filter should pump 1/2 the pond volume every hour, in this case a 6000 lph pump will be fine. Larger pumps would be needed for a heavily stocked koi pond, which would mean a scaled up UV and filter box will be needed to cope with the faster flow. ie if the pump was 12000 lph then the filter would need to be for a pond twice the size as would the UV.

The filter box should be one rated for a pond of your size (in this case a 12000L pond) or one of a larger size will help do the job better even if the pump is still only 1/2 the pond volume per hour.

For UV filters a basic rule to follow is 10W per 1000 gallons, but the more the better, so a minimum UV for a pond of the size in the example would be 30W, but a larger one would prove more effective as the algae would experience more exposure to the UV if the pump size was still the same. Shallow ponds would need a higher wattage UV as they are sun traps so would need more UV to kill the extra algae that would grow. UV filters only clump together suspended algae, blanket weed wouldn't be touched.

If you have any further questions please ask in the pond section