I'll have to give the build a try before final verdict. Overall, your guide is lacking though, you should check some of the other builds out there to find a good style for you. But your description just isn't descriptive enough :).

I don't like to give thumbs down votes, so I'll just leave it alone for now :)

i admit that this is not the best team battle build it is ment to survive in a side lane/jungle to farm up faster for the late game, getting the gunblade is key, i normally get mine within 10-15 minutes or so, if it takes any longer than that at least make sure that you have your cutlass, after that jungle/gank until around level 11. by then you have provocted enough of the people (by chasing with ult) that they will target you every team battle, at this shift in the game when people are typically team pushing, i stay in a lane and farm / gank the enemy carry. i have not hit level 30 yet so it might be short-sighted build in that respect, but so far it has worked marvels for me.

i suggest if you see a team battle coming, move into a position that you will be able to blink to your target (typically a caster, so you can silence and make them useless) without having to run around, wait (patience is key) after the initial abilities have been tossed out and your team mates have engaged the targets, thats when you blink behind and kill a caster / blink out. it causes extreme confusion amongst the enemy team and that will allow your team mates to come in from the front and break the line. typically you would try to catch someone running up to the team battle so that you have enough time to get out before you have 4 people running at you.

P.S. this is a carry build, not an AP build. for those who want to play kassadin as a melee instead of a caster. i always find it fun to launch null sphere + rift walk onto target + ignite/gunblade/nether blade, then procede to shred my target.

I don't think hybrid Kassadin is a good idea since his AP burst is one of the highest bursts in the game. and kassadin shouldn't stay in battle and lifesteal/attack speed require stasying in battle.