Kassa's build.

Hello guys.I 'm gonna tell u a built for kassadin
.When i play kassa on mid,i usually take boots +3 healing easier to move and u can last hit without taking damage from the opponet.If u wanna have some hp you can take Rod of Ages.(catalyst is very usefull for early game,and Rod of ages is an item that helps a lot on mana and hp specially.)Now if you want to go full damage grab catalyst Void Staff and Then rabadon's cap gives u lot of a dmg. If you want ap+some mana catalyst again core item and tear of goddess goes for archangel's staff is pretty good.Mana regen + a good amount of ap.On your Runes.you need Magic Penetration,A little ap(like 20)And some cd's runes.You don't need mana regen cause you have W's passive.
Kassadin's Full built is:boots of penetration,rod of ages,Void Staff,rabadon's cap,Archangel Staff And the last one depends from the opponents :)
Thank ya a lot <3