The game now assumes that most PCs won't take weeks off from adventuring to make mundane items, so there are no rules for it in the core books. That doesn't mean they won't be included in a future supplement, but for now we're in house rule territory.
If the player really wants to wants to make it themselves, then off the top of my head your options are have a week or two of downtime, have that character absent for an adventure, or have some sort of skill challenge.
Personally, I'd remind the player that this will take a week or two, and have have the local blacksmith offer to make the suit up if the party just take care of this little problem...
In any case, the party should hopefully soon find magical armour superior to what anyone can craft with materials like kobold scales.
The 'special' refers to the masterwork armours. +4 and higher armours are never standard armour - that breaks the maths. Instead, there are two grades of masterwork for each armour category - one for all +4 and +5 armour, and one for all +6 armour. (The books don't explicitly enforce this, but
the official FAQ makes it clear.)
Unfortunately, it seem that it is up to the DM how to enforce this - either enchanting armour past its enhancement bracket fails, or else it can upgrade the base armour. Also, the DM has to enforce that these masterwork armours cannot be used without being enchanted to the relevant standard. All in all it's a bit of a pain - IMO the rules should have included a default way of explaining all this.
