How to create a class-level-defined monster

Question

I would like to create some small groups of kobolds for my players to tackle with. The idea is to have some "standard" kobolds copied directly from the Bestiary 1, but to also have some "special" ones with some class levels in fighter or sorcerer (and also "intermediate" ones with adept or more warrior levels).

I found the "Monster Advancement" page, but this is a description to add class levels to monsters that otherwise only possess racial hit die (Trolls, Giants etc.)

So, does this work exactly like creating a player character? How do I determine ability scores? The Kobold Warrior 1 listed in the Bestiary 1 seems to have had Str 13, Dex 11, Con 12, Int 10, Wis 9, Cha 8 before racial adjustments (A 3 Point Buy, if i calculated that right)

How do I determine CR for a Kobold with added Class Levels? According to the Monster Advancement page, adding a Class Levels adds +1 CR if the class is "key", otherwise only 1/2, also only 1/2 if its a NPC Class. Shouldn't the Bestiary I Kobold Warrior 1 then have a CR of 1/2 (because Warrior is a NPC Class) instead of 1/4?

Answer 1

You'll want to use the Race Creation rules from the Advanced Race Guide.

A link to the SRD for reference: Creating New Races

Also, I see you specifically mentioned Kobolds, who have a stat block for making PCs with them (and thus making NPCs as well). Kobolds are a 5 RP (in comparison, humans are 10) race who had their stat blocks printed in the Advanced Race Guide alongside the rules for creating custom races. Kobold Stats

Another thing to note is that the stats on the Kobold you linked already have a class level (Warrior 1, an NPC class) You could power one or two of the up by swapping that class level to Fighter instead (essentially granting them a bonus feat) and maybe adding one more level of Fighter (for one more feat).