There's three sizes in RoH: small, medium, and large.
Some armor and weapons are a specific size, but many aren't.
It seems strange to me that what a halfling can wear, a troll can wear as well. Even within a size type, there are differences. An elf and a dwarf are both "medium," but the elf is taller, and the dwarf is stockier.
I propose that a new command be added, called "fit." You would go to an existing smithy:
fit boots saalventhis
Saalventhis the Dark-Smith fits the dwarven tempered boots to your size.
or
Oops! Sorry lad, broke another one! Saalventhis takes your money.
Should be very similar to "repair" or "fix", in the pricing of fitting armor, and whether or not the smithy succeeds or breaks it. Thus, the smithy's skill level will be important.
The pricing can also be based on how good the armor is, not only it's original value.
The advantage of fitted armor? Add 0.1 to the AC value of the armor. Alternatively, decrease 0.1 from the AC of all armor until fitted.
look boots
They are pretty small.
It is in excellent condition.
Your armor has been fitted.
Some armor can be made to be impossible to be worn unless fitted. If you take someone else's armor, then you would have to refit it, if possible.
Or:
You see Jimmy the Orcish Smithy.
fit dwarven jimmy
Jimmy the Orcish Smithy refuses to fit your dwarven tempered boots!
Jimmy the Orcish Smithy snarls, "Get that out of my shop!"
Jimmy the Orcish Smithy attacks you.