HELLO welcome to my first mobafire build with kassadin!my build excels in AP=Ability power rabadon deathcap:excels in granting you more AP
lich bane:passive:after you activate a spell it hits an auto attack equal to your AP
mejai's soulstealer:stacks up 20 stacks and for every stack it gives you AP
hope you like it and am not a pro but please comment and if you have any question just comment

pros:
.runs away easily by the ulti
.not targeted in team fight like tryndamere
.2.6 seceond cooldown of silence

cons:
.squishy
.weak in early game
low base HP

null sphere:is really important because,it silences your enemy for 2.6 seconds and adds a heck of a burst damage
nether blade:you use it in 1v1 mostly(my opinion) becuase it grants you armour penatration
force pulse:slows enemies and add damage which is really great
rift walk:its like flash but a 5 second cooldown you can run and get enemies

kassadin is really effecient in team fights he slows enemies and silences them which is a big advantage for your team and rift walk does damage to your enemies,but be careful if you get targeted run because he is really squishy slow them and use rift walk

all of them grant you motr AP except the marks which grants you armour penatration its good against tanks

rift walk is an amazing ulti so as force pulse
force pulse:slows
riftwalk: gets enemy or running away
you can use it as a combo for running away or getting any enemy

flash:is important for tower dives and getting away
ignite:to get an enemy

kassadin is squishy so try to get vision wards in order not to get ganked and always play safe in early game because he is SQUISHY and, mid game if your are fed try to get kills to get more stacks and become more fed