Notes:

The class specifies Rokugani steel but any metal will do, if you're not using Rokugan. Koku was changed to gp, they're equivalent. Also Superior craftsman's ability text was the exact same as exceptional craftsman in the book. It was likely supposed to be an intermediate between legendary and exceptional, so I adjusted it as appropriate.

Rokugani steel is as normal steel except, it's treated as masterwork for the purpose of crafting, this does NOT affect armor check penalties. It has a natural enhancement bonus that doesn't stack with any other bonus, but functions in areas of antimagic. I.e. it can function as a +1 sword for the purposes of overcoming DR, if it's of fine quality. The object needs to mostly be made of the metal to get the bonus.

The following bonuses are based on the grade of Rokugani Steel

Fine - +1

Exceptional - +2

Superior - +3

Legendary - +4

Tools crafted of Rokugani steel give the appropriate bonus on skill checks based on the grade.