Ooohhh, ops :S

I forgot to recommend marks >.>
In marks you should definitely go with Magic Penetration. They are the best choice.

You won't be needing the mana anyway with a mana crystal in the beginning.

Np, happy to help ^^.

Gotta mention that lately though, I've been using my mana-reg/lvl seals a lot. Mostly since facing someone with good reg(like Heimerdinger) in mid is a real pain in the ***. Heimer is free now and I see a good one in half games i play now..(though never in my team ;( ) Really irritating with his good hp-reg.
And btw; I go mid most of the time.

But do try out the things i mentioned, they're perfect for me :)

oke nice not much experience kassadins running around... i efen see people not efen knowing how kassadin play at all.... Thnx for the tips. SPelling aint my best side and this is my first build:p Though i like the way i play just got a 16/4/10 again so im kinda happy with it. THough improving is always nice:)

Ty

I've got 151 matches with Kassadin to date. So i've got some experience playing as him ^^

I think you should definetly go with 21off, mana-reg/lvl seals(optional) and a Mana Crystal if you have no mana problems. 21util is for those who have mana probs :P. The 5%+dmg is a big bonus and after a few levels you get more mana-reg from this than from the utility specc. Getting offensive mastery helps you with lasthitting too.
Personally I get hp/lvl in seals. To reduce kassadin's "squishiness".

Oh btw; I just got the impression of the "luck part" that from this sentence:
"My style might be weird or lame atleast it works for me. With this way of playing i useally do not die more then 5 times in a fight. unless it is a totaly fck up."

Kinda unnecessary sentence, and it's got loads of misspellings :P
(too quick to judge, I know >.> )

You got most things right, but the marks and seals are definitely wrong..
And the first item should rather be mana-reg/mana than ap. *Edit :S*

Well for me this build is more about controll then luck. For me i controll the game..
What marks/seals do you suggest then?
And about mana-reg/mana item i don't know. i never rlly get oom. when i get i can recall and get a new item. and im full mana again. With the AP i can controll them better. But thats just the way i play ;)
Ty anyway for you comment