The runes you are going to use for the Ability Power build are , Magic Penetration Marks, Ability Power per level Seals, Ability Power per level Glyphs and Ability Power per level Quintessences.Why should you use these Runes?Because Evelynn has been nerfed and her base stats arent the best, so all u can do is to focus on mid-late game which Evelynn shines better anyway.

Masteries is one of the most important things, so you have to use your points wisely.I like to use 9/0/21 since you need CDR(Cooldown Reduction), extra Ability Power, Mana regeneration and Magic Penentration.Changes can be applied at the Utility tree, but please guys dont even think place a point on gold per second.

Flash: I believe its the best for chasing,escaping, or even tricking a melee fighter!Some of you might wonder how you can trick specialy a melee fighter with Flash.Lets say its an 1v1 fight and you both have low HP left...you Flash behind your opponent, confusing him with your move.Your enemy usually wont be able to react fast enough ending up dead!When im in a situation like this I usually do it when Im sure it will work.
Note:This doesnt work always because people have different reflexes.

So, about Ignite.Its a great Summoner Spell for Evelynn because it works really good with your Q, Hate Spike.Of course this isnt the only reason you should use Ignite, it also deals True damage,its very good at finishing off your opponents or ensuring a kill and its great against enemies with Spell Vamp or Lifesteal.

1) Start off with a Doran's Ring.

2)Continue with Amplifying Tome.

3)Take Boots of Speed or finish your Mejai's Soulstealer.

4)Buy the Sorcerers Boots.

5)Start building your Lich Bane, remember always start with Sheen.

6)Finish your Lich Bane.

7)Now you should buy either Blasting Wand or Needlessly Large Rod.

8)Complete your Rabadons Deathcape.

9)Now you can buy Rylai's Crystal Scepter or something like Abyssal Scepter.

Core Items:Mejai's Soulstealer, Lich Bane, Sorcerers Boots.

I hope you like my Evelynn guide, what can I say...Enjoy to the Fields of Justice!