This is a build guide for Evelynn. I made this build for one of my friends that I play with who just bought evelynn. So far I've tweaked this build multiple times already, however I have not changed any skills, I just reorganized them.

My friend so far has been very successful with this build, I myself have not played it I just created it and take his feed back. However; I have played at least 5 games side by side with him as evelynn so I have first hand experience seeing what happens to Evelynn.

Greater Mark of Magic Penetration: This magic penetration is very handy because Evelynn's Ravage spell is increased in damage by 100% of AP, therefor the magic Pen will do even more damage.

Greater Seal of Scaling Mana Regeneration: This seal will increase your mana regeneration which comes in handy when you have to hold a lane or when you are in a lane for a while.

Greater Seal of Replenishment: Pretty much the same thing as the seal of clarity, except this is right off the bat where as the seal of clarity is per level.

Greater Glyph of Scaling Ability Power: Give you extra Ability Power, enough said.

Greater Quintessence of Scaling Ability Power: Gives you extra Ability Power, enough said.

7-0-23
This means I place seven(7) points into the offensive skill tree and twenty-three(23) points into the utility skill tree.
The utility portion is for stuff that would enhance Evelynn's mana and mana regen, the main reason for going down the offensive tree is to get the cooldown reduction.

Mobility BootsBoots of Mobility: OK, so Evelynn is an great character to use these boots with because she can get in and out of combat very easily because of her invisibility, also she is a ganking hero(at least with this build) therefor being able to transverse the map very easily and quickly is a key priority.

Blasting WandBlasting Wand: Evelynn can not do a lot of damage if she has no AP, therefor getting this blasting wand is very important if you want to progress well enough through the beginning of the game.

Rod of AgesRod of Ages: this item is going to be important for surviving in lane because it gives health and mana, in addition to more AP. Basically this item will keep you in lane long enough to not have to worry about recalling to heal or get mana.

Zhonya's HourglassZhonya's Hourglass: This is your tank item, Zhonya's Hourglass is going to be important for surviving ganks on you, and ganks you make. Also now you don't have to be stealthed to entire combat with minimal damage.

Rabadon's DeathcapRabadon's Deathcap: AP,AP,AP,AP. This item is your AP, from now on whatever AP items you get give extra AP, so basically more damage!!

Void StaffVoid Staff: AP and magic penetration, your AP skills now pierce more magic resistance, Isn't that good.

Bilgewater CutlassBilgewater Cutlass: This item seems unorthodox, for a reason... IT IS!!, because the next item is going to be your last item, getting this item first is more cost effective.

Hextech GunbladeHextech Gunblade: This is the item that will make you great in lane, the main point of this item is the spell vamp and AP!, however; the activate skill of the Hextech Gunblade is pretty cool, it does 300 damage and slows down the enemy.

The only really important level-skill choices are:
Level 1- Shadow Walk
Level 2- Ravage
Level 6- Agony's Embrace
Level 11- Agony's Embrace
Level 16- Agony's Embrace

The rest of the levels are not as important, but those 5 are, so just pay attention to the match at hand and choose spells accordingly.

Flash- I suggest Flash because it's great for getting in and out of combat in dire situations.

Ignite- This spell is great for that enemy that is just of of your grasp, cast this as an enemy runs towards a tower(only if the enemy has low health) and watch them squirm.

Evelynn is great when paired up with a tanky dps that can distract enemy champions, take a lot of damage and pull the enemy champions out of cover.
When Evelynn's lane partner gets an enemy champion isolated, evelynn needs to jump into combat stleathed and drop ravage on the target and use hate spike as they flee.

Pros:
Evelynn does massive damage with her ravage
Evelynn's Hate Spike has a very short cooldown and can almost be spammed
Evelynn is great at ganking
Evelynn is very scary to enemy champions

Cons:
Evelynn is squishy in the beginning of the game
Evelynn steals kills(therefor her lane partner might get mad)
Evelynn is not Chuck Norris

Evelynn is a versatile character that when she focuses on a single style of play can be extremely deadly. Beware...
Please comment rate and suggest.