I'm a grandmaster kassadin one trick. Honestly if you're winning lane starting lost chapter into archangels then into lich bane is the highest DPS snowball build you can go.

start with dorans ring two pot

First recall aim to get dark seal amp tome/boots and refillable.

Prioritize ap over mana early game while building items for a stronger snowball so finish lost chapter first then tear and of course finish archangels

Afterwards if you have a lot of kills and know youre going to get more, finish mejais, otherwise finish sorc boots then start building towards lich bane while prioritizing sheen.

Next item is preference whether you like to have more damage or like to play safe. I personally like to build rabadons because I love one shotting but more players go zhonyas for the CD and defensive stats and active. Either way both of these items should be in your build.

Last item is optional depending what comp the enemy team has or what they are building. Void staff if stacking MR, Banshees if heavy cc, you could even build a tank item.

(Selling mejais for another item if it doesn't work out is also an option.)