||I am thinking about buying (or building) a compressed air dryer.
||
||Any suggestions?

An old refrigerator with a heat exchanger inside (coils of copper tubing) ,
air
enters and exits through the side walls of the fridge.


You would also need something to get the condensed water out of the system.
Usually, a ping tank with a drain valve will work. The water will collect at
the bottom of the tank and it will be spit out when the drain valve is pulled.

Another option would be an air dryer used in a pnuematic truck brake system.
The only one I know by name is the Bendix AD-4. The problem is that it might
not have the capacity for the amount of air you would need.