Step 1: Gather materials and plan!
To build a liquid cooling system you will need:
*A radiator of some sort. I used a heater core. specifically, one meant for a 1977 Bonneville with A/C. You can use pretty much any other type of radiator or heater core, but my recomendation is to stay away from the aluminum ones. copper or brass only is the way to go. having mixed metals in the loop can cause galvanic corrosion. the purpose built radiators commonly available at stores like frozencpu or xoxide are great too but expensive. heater cores are able to work as well or better and only cost 25 dollars or so.
* A pump. I used the danger den 800L/hr model. other pumps will work but keepin mind flow rates and noise. This pump pushes a lot of water almost silently, so its worth the money that I paid for it.
* wood. I used 1/2" birch plywood. this is great if you are going to stain or paint it black like I did, but solid wood would also be nice.
*fans. I used 4 cooler master r4 120mm fans. they probably are not near the 90cfm they are rated for, but they still push a good amount of air, and are relatively quiet. I used 4 so pricey fans will definitely add up. these are available for about 7 bucks each if you shop wisely. 120mm fans push the best air vs noise ratio, plus they are ideally suited for the size of my heater core.
* A reservoir. Mine is made out of a piece of clear PVC. Use your imagination, I am sure there are lots of other things that could be used as a reservoir, I just can't justify spending 40 bucks on a plastic container.
*hose barbs, vinyl tubing. I used 3/8" ID tubing, but half inch works well too and increases flow rate.
*assorted screws, bolts, scrap aluminum pieces, switches, connectors, leds, etc. you can personalize your system any way you like. I will probably be adding some UV leds to make the coolant reservoir glow, but the sky is the limit here.
Once you have gathered your Materials, its time to plan out the dimensions and structure of your enclosure. I decided four fans in a Push/pull configuration would afford the maximum airflow through my radiator. a separator divides the box into the "wind tunnel" section and the pump/ power section. a slight groove in the box retains the radiator. If you decide on only two fans, they seem to be more effective at pulling air through the radiator than pushing it. perhaps placing the radiator near a large vent and four fans pulling air through the radiator and out of the box would be more effective, or two smaller radiators mounted in the ends of the box with four fans exhausting air out of the box. The advantage of my setup is I can selectively turn off a pair of my fans. Once all of the details have been ironed out, begin cutting the wood according to your plans.