Hey all,
I'm Alidonis and I am writing this guide on Evelynn. This is my first guide and I do not know how to do all the fancy stuff you would see on a guide, but I am going to go as much as I can from the few months I have played Evelynn.

Evelynn is regarded as one of the worst champions in LoL and most people rage when you want to play her, however, the do not realize the potential Evelynn has and how she can carry the whole team and make the other team rage.

Pros:
Amazingly hard opener
Very fast
Good ganker
Can be a good team fighter
Fun to play
Watching people rage

Cons:
Squishy
Oracles Elixir shuts her down
Can be a bad team fighter
QQ'ed about all the time

Greater Mark of Insight x9
Greater Seal of Force x9
Greater Glyph of Force x9 or Greater Glyph of Insight x9 or Greater Glyph of Alacrity x9
Greater Quintessence of Force x3 or Greater Quintessence of Insight x3

I am a firm believer in not wasting an money on items that you will sell back later. This just makes it harder for you to complete your build and just seems like a waste of your money.

Items in bold are items that are part of the build

Start off with Boots of Speed and health potion x3
Next get Sheen for its amazing passive
If you have the money get Kage's Lucky Pick (This helps with gold income)
Boots of Mobility (for complete map dominance, also good for escaping)
Needlessly Large Rod
Rabadon's Deathcap
Lich Bane (take MR first if heavy AP team)
Void Staff (gives good MP)
Zhonya's Hourglass (Gives extra armor so you won't be as squishy)
Deathfire Grasp (Greater Active Ability and the CDR is nice for Ravage)

Hate Spike-lvls 2, 7, 10, 13, 14
Shadow Walk-lvls 1, 8, 15, 17, 18
Ravage- lvls 3, 4, 5, 9, 12
Malice and Spite-lvls 6, 11, 16

This is how I play Evelynn, I realize everyone has their own play style but this is the best way I have found to play her.

First of all, if you have a jungler, call solo top. Whaaaaaaaat?!?!? Eve solo top??!?! Thats crazy!!! However if you coordinate with the jungler and request lots of ganks you should be fine, however they will push a tower in the first 20 minutes but the pay off will be great. Play defensively!

Start by taking Shadow Walk, this allows you to scout bushes before minions spawn and it has a slow when you open up on a champion.

Next I take Hate Spike, this helps in farming to increase your level.
Levels 3-5 Should all be devoted to Ravage, this gives you an extreme advantage over your lane enemies.

When coming up on an enemy activate Shadow Walk. When you are in range of the enemy activate Malice and Spite and then open up with Ravage. This slows the enemy and usually the damage is so high the enemy will panic, after using ravage spam Hate Spike 2-3 times and then use Exhaust, Ignite and Spam Hate Spike again, use Ravage when the CD is up.

More tanky enemies should be engaged with a teammate

In a team fight, Evelynn can go two ways, either she is focused right away or forgot about.

Wait for your team to initiate the team fight. Look for people running away, off to the side or the one your team is focusing. Open with Ravage, hit them with Lich Bane proc and run out spamming Hate Spike, and then repeat.

So this is my guide to Evelynn. i hoped that you liked it and I know it is probably bad but it is my first guide. Hopefully ya'll can give me some constructive criticism to improve on it!!! Let me know how you like it!!