Originally Posted by BuceTheCaboose
Always rush Catalyst; it will help you sustain somewhat in lane and give you a good chunk of health. Rush RoA as fast as possible. Next, go for Deathcap for damage. After that, it's situational.
My typical Karthus build looks like:
Rod of Ages
Void Staff or Abyssal (I lean more towards Abyssal)
Ryali's Crystal Scepter
This guy, you want to follow his build, i do exaclty the same thing, but i go boots, rod of ages, void staff, death cap, ryalis, hourglass.
Karthus is actaully an amazing farmer, you just need to practice more with his AA. Just keep in mind that his Q does more damage when it hits a single target.
So to max out karthus in his abitlity to lane, i HIGHLY suggest getting -
3 Flat AP quins. 9 AP per lvl Glpyhs. 9 Armor Seals. 9 Flat AP Marks.
Masteries - 22-8-0
With that, youll have some durability and increase your damage output.
Also, remember that a Mana Karthus build, is also viable, being able to spam your Q and your E in the middle of a team fight, can cause massive damage.