I found out what the guy in the other thread was talking about. It is in the OA FAQ on page 3.
So I guess you can make a Masterwork Mithral plate suit. So I guess that would take about 6 weeks on top of making the normal suit. Goodness.
Mithral lessens armor check penalties by 3. (See page 243 in the DUNGEON MASTER™s Guide.) The minimum armor check penalty is 0. The reduction for mithral and for masterwork stacks.
So I guess you can make a Masterwork Mithral plate suit. So I guess that would take about 6 weeks on top of making the normal suit. Goodness.