just check Azirmains reddit. They have like 4 or so builds they go by.
1)The standard build in game,
2)One focused on max damage where you replace rylais with liandry's torment, but get void first after having gotten nashor's (when you need to hard carry)
3) Attack speed build where you get AS boots over sorc, which gives you better waveclear, slightly less damage on combos but better overall DPS
4) normal mage build which is where you get morellos and is good for lanes that shove you hard and where you need a lot of mana to deal with then and damage for trading early, at the expense of your lategame. (but you already have a really great late game and it won't dip by much so it's sometimes worth it)
Just practice csing, knowing when to shove, and learning when you have lethal and executing on it properly (which is the hardest part)