Really depends on the core you use (the magnetic permeability). The number of turns depends on the core material and size of the core.
I see you are asking for 50mH at 6 amps. Maxim chips? Pull the data sheet on the 724 part and you'll see that this 50uH (micro not milli) is not critical.
Go buy these $2.99 inductors from All Electronics is Los Angeles. 100uH at 9Amps. They'll work fine.
Wouldn't you know it, I can't find my flyer from them. Call them up and ask them about it. Much cheaper than buying the 50uH 9A ones from Mouser or Digikey.