Ghost
its really good to chase down people with and if some one gets an oracle(which they will most likely do) you have boots of mobility so you can run in there before they can even react.
Ignite
I love this spell i use it alot with other champions, for Evelynn its hard to get kills early game without sheen so this sorta insures the kill.

I get shadow walk first so i can scout ahead and stun so my other teammate can help kill.
Then get ravage this is without a doubt the best ability ever it does a ton of damage, when i'm stealthed I always lead with that ability unless if its a 2v1 you do hate spike because it hits 2 targets and stuns them both (I wouldn't 2v1 unless if your fed).
its really hard to get any kills without all you abilities so get them all ASAP.

you start of getting Sapphire Crystal because it will help you stay in lane longer until you have enough for sheen. I cant express how much you need sheen, Its amazing for Evelynn because hate spike has a super tiny cooldown so you spam hate spike and you have sheens unique keep coming so you do ALOT OF DAMAGE.
Boots of mobility
This helps you get to places quick and easy, if someone has an oracle your going so fast that they cant even react and then you own them.
Majai's Soulstealer
this is great because Evelynn is an amazing last hitter so her stacks go up pretty fast.
I'm going to skip going into detail about the other items besides Rylai's Crystal Scepter i dont know if you will be able to have enough money to get this far but it helps you because it slows the target down so you can keep on attacking them.

Thank you for reading hope you all like the build and would like to hear some feedback.