My 1st Filter
My 1st filter consisted of 5 -45 gal barrels that were purchased at a wine store.They are connected to each other using 4'' toilet bowl flanges
These are screwed and siliconed into place.They are connected in a bottom, then top pattern. There are 11/4'' valves in the bottom of each barrel for cleaning.
In the 1st barrel, the water has to pass through plastic garden netting. This holds onto the heavier solids.
The 2nd barrel has 6''of open pore foam, cut to fit the barrel. This is on top of an egg crate shelf about 15'' off the bottom.
These 2 barrels act as the mechanical part of the filter and are cleaned at least once a week
The 3rd barrel has 9'' of Japanese pads, each pad is separated be a piece of egg crating, to help with water flow. Again, these sit on an egg crate shelf. 
Barrels 4 and 5 have about 4000' of PVC ribbon in them. These 3 barrels are my Bio-filter and are rarely ever touched.
The blue box, a 40 gal Rubber Maid tote, that sits on top of the last barrel is a Trickle Tower. It has a piece of egg crating that sits about 2'' off the bottom and the box is filled with " synthetic" floor polisher pads. These are in two densities and seem to work really well. They're cheap too! The drain in this box is a shower stall drain, about $10.00 at a hardware store. Part of the water flow for here comes from a 600 gph pump located in the 3rd main barrel. The balance, 1500 gph, comes from my UV pump, (40w Aqua)
The main barrels are fed from a submersible pump, pumping about 2000 gph, located in the main pond. All the water ends up in the 5th barrel and then is gravity fed back to the water falls via a 4'' pipe.
The main water feed to the barrels has a couple of valves installed that allow me to bypass the filter and the UV if I have to treat the pond for any thing.
It's not the prettiest thing, but it can't be seen and the whole thing couldn't have cost more than $500, including the Japanese Mat and that stuff is expensive. Needless to say the pumps and the UV were extra.