Well, this build is just for the ones that might love to play with champs that can riftwalk, use a fuc**ng nether blade and also deal heavy damage... you know about who I'm talking about... Kassadin can and is a awesome champ even for the ones that are just beggining to play the game (you know... the noobs).

"I will kill you so fast that you wouldnt even know how I did that without hacking programs!" ROTAKURULEZ.
"Believe me... this build is freaking awesome" Laubenstein.
"WOW!" vitinhobla.

Runes

For KASSADIN runes I got Attack Speed runes and Ability Power Runes, you know why? Because if you are here you can see that this build is for his second skill, and if you want heavy damage and fast kills, you will need just that runes.

Explanation about the Runes of Attack Speed

This runes are awesome for him for only one reason... It makes him deal heavy damage when you active Nether Blade and makes him heal his mana as faster as spawning pool (believe me, thats the truth).

Explanation about the Runes of Ability Power

I won't have to say lots of thing about this runes if you play Kassadin as longer as I'm, but if you see his Skills you will see that is essential for him these runes.

Masteries

For his masteries I got the ones of offense that reduces his cooldowns, and the ones that increases his attackspeed, making his ulti and his second skill much more offensive. And I also have goten the masteries of Utility that makes him faster with better cooldownsm and a great mana regen and a little bit better health regen, and obviously I got the masteries that makes his death a little bit shortier.

Items

That's the better point of this build and the point that makes it the better Kassadin build for me, I will explain why with a story...
One day I was playing kassadin and decided to make his second skill great, because everyone that plays him say that that skill is his worst skill, but I tryied to make these guys shut up and got some time studing his skill and wich itens would be great for making it better. After sometime of researches, I finally tryied something new, making him deal poison! How? I will explain my friend, you know that item that was at the beggining the best item of lifesteal? Yeah my friend, Malady now is made for Kassadin, why? Just because it deals the same thing that his second skill does when activated, almost the same thing xD, I mean it makes him deal his damage + some magic damage. And thats where I've started making his items build, so I found Wits End, wich one makes his bonus damage heavyier, and then I finally got the Executioners Calling, wich ones reduces healing percent of the target too and gives kassadin lifesteal!! Isnt that freaking awesome fellas?
But I still felt that something wasnt good for him, so I got Archangel's Staff, wich one makes his mana larger and increases his ability power, meaning more damage for kassadin :D
Finally you will have two options of itens: Panthon Dancer or Rabadon's Deathcap. I always think like this, if you want to deal more damage whit your second skill, get Panthon Dancer, if you want more damage with your first and and third skill, even the others hahahaha, buy Rabadon's. But I still prefer Panthon Dancer, because you will have movement speed increased and Attack Speed.