Nah not good. Really bad build

Deathalo44 is right man. AD Karthus IS a troll build, weither you accept it or not.

I just hope you'll actually LEARN not to be so lame in pretending to be chancing upon my build to downvote, despite obviously I have included in a section in my builds asking for USEFUL CRITICISM or an upvote with some more USEFUL CRITICISM.

The only skill that syncronises with Karthus AD is Wall of Pain. I was giving useful criticisms without downvoting, in hope that I can see some improvements THEN upvote it. Your lame attempt at downvoting my guides cause I downvoted yours is lame.

Lemme give you a few examples.

Tristana. What makes her a good AD carry? She can chase via Rocket Jump, she farms wayyy better with Explosive Shot, her attack speed gain from Rapid Fire and Draw a Bead makes her a good AD carry. All her skills syncronises with her role as an AD carry.

What makes Amumu a weak attempt at being an AD carry? Despair does magic damage in % with no AD scaling, Tantrum is weak especially if you have to invest a lot in tanky items, your ult has a really long CD to help much in skirmishes, and Bandage Toss will probably get you killed in teamfights.

What makes Rammus a decent-good attempt at being an Tanky DPS? Powerball allows him to chase. Defensive Ball Curl gives him survivalbility and complements with Puncturing Taunt, which gives (I bet you won't read this)you an extra edge against people who try to run. Your ult does help destroying towers, but is quite useless in skirmishes. His Spiked Shell converts armor to AD, syncronising with Atmog combination, especially since most tanky DPS gets it.

My point here with this 3 examples is, roles. Karthus role in teamfights is magic damager, focusing on killing everyone. Killing him early in a teamfight may not help much, as his Death Defied will bring him back for a few seconds to dish out revenge. Lay Waste with Wall of Pain ensures a lot of damage for an AP, as well as the AOE from Defile causing massive damage in teamfights. My suggestion is learn how to play Karthus really really well, then try making a guide on him better. There is no point sticking to the crowd and next to copy-paste an entire build as it won't help much, nor is it that much to go out of your way to include in non-complementary roles.

That being said, I still won't downvote you. Starting a downvote war is totally a waste of time, and thats probably what you already started.

Yes I can deal tons of damage without suiciding and for damage as you do in your AP Karthus build. I deal 400 damage with every attack and 1000 with every crit with lifesteal on the AD carry Karthus build (second one). And on the first one you have lots of health and can be dps that can tank a bit. The ulti still takes down the ones with that low health when it does 600 base damage. And Defile deals around 100 damage every second + my basic attacks.
In late game I don't use the Lay Waste and it also says in the text if you would have read.

PS : My Karthus build can deal roughly 1.5k damage per target with my ult, if penetrating most of their MR. Can you do roughly the same?

PPS : My Karthus in teamfights does over 350 damage per second AOE with defile. Can yours?

PPPS : My Karthus does over 400 damage per hit with Lay Waste. Can yours with normal attacks?

Ditto to lifebaka.

Your Q interupts your normal attacks (You must cast before you start shooting your beam). Your E is weak, unable to do much.
Your R is pointless. Better used as a poke
Your Passive is totally ****. It doesn't even help.

ONLY your W synchronises with you. Its not like the case of AP Sion, who was Stun and Shield for damage, Enrage for HP (Killing with spells count to HP rise), ult for fun. Karthus is naturally a useless AD no matter what format you play him as.

Try it out and you will see for yourself. You can deal more damage with basic attacks + Defile than ap karth.

Karth's abilities don't lend themselves well to being an AD carry. This build is, mathematically, significantly less effective than playing Karth AP. Troll build or not, it's not good.

That's because you haven't tried it yet ;)
I have to agree to that, it doesn't seem like it could work but it actually works but since it seems that bad there will not be lot of players who will test the build 'cause of that.

Loled hard!!!.It looks very silly x).