I haven't voted yet, and here's why:

1) Your guide contains only text. If you would like to learn how to bbcode, check out jhoijhoi's how to make a guide : http://www.mobafire.com/league-of-legends/build/making-a-guide-101506
This is where almost all the newbies on mobafire go to learn how to bbcode

2) You have a no-AP build, meaning you buy your very first AP item quite late into the game. Karthus is heavily reliant on AP, and although he is a late game champ, he needs AP in the early game as well.

3) You only have one build. There are multiple ways to build Karthus. You should recognize this in your guide.

4) Your build does not include Void Staff--an item essential to Karthus for his ult and lay waste.

Once you fix up your guide, PM me and I will re-review your guide :)

Okay,

First of all, it's Karthus, with a 'u'. Spelling a title wrong immediately puts you at a disadvantage. You will also need to learn BBCode as on Mobafire this is pretty much a requirement for any guide to succeed. I hope you'll find this useful. If you're still hung up on ideas feel free to check out mine for inspiration. I know you might not have a lot of time as you mentioned in an earlier comment, but I can honestly say that you won't get anywhere without a standard guide layout.

Hope I don't sound too harsh. I upvoted and wish you the best.

I just give the idea of buying cooldown stuff instead of your archangel staff because it's not really usefull to buy 2 ... and I know that karthus can also be played in cooldown regeneration but I play a Karthus based on AP like you ;). For the BB code it just take you 5 minutes to learn the important thing and be able to make a well presented guide look here. I hope that will help you to make your guide better :).

Hey, I'm only doing this in my very spare time, I don't even know what BB code is. I find that cooldwn on Karthus's ulti isn't actually that important late game and that blue buff, Masteries and Blue pot give you enough cooldown reduction. My Karthas relies mainly on Defile doing roughly 500 a second and his ulti does over 850. With my build i reach more AP then if i had a death fire or Morrelo's is added by more then 100. The Mana regen runes are for early game and give you literally unlimited harass, not stop spam it's still almost impossible to run out of mana. I would be interested in seeing your guide especially any strategies you know that work well. Cheers for feedback.

I don't really like your stuff ... I would take the rod of ages before the Rabadon and the second archangel staff is useless because you don't have the time to make skill for his buff ... You nned couldown reduction like the deathfire grasp or the Morello's Evil Tome for kartus ulty and his cc spell. But there is some good points : your masteries are great, the runes sound good (I would take some magic resistance instead of mana regeneration runes because if you go on Tear of the Goddess you don't need to have more regeneration mana, you also can take the blue buff). Good skill sequence, in fact that is the good one with kartus ! Maybe you also can tell about the Zhonya's Hourglass wich can counter kartu's ulty ! You also need BB code to make your guide easier to read. I haven't voted yet because I think that when you will fix that problem your guide will be pretty nice :). Iwill check it soon

One more thing, I am also working on guide for kartus I tjink I will finish it in 2 weeks are something like that. I will show you to be able to compare with yours.

Mad build. Win heaps of ranked game using pretty much same build. Interesting flash strategy. I reckon that that could be a real game changer.
P.S. the reason i only been on once is coz i can't remember my old account :D
P.P.S needs pictures