This guide will show you the money. Literally! All gold per time items, runes and masteries are heavily abused in this build to rush you your high-priced items so that you can buy your way into mid and late game easily, giving you the advantage. While in stealth, you'll be making money. Smite on recharge to gain even more money. Buy your gold per items to make even more money! Proc minions and last-hit everything you can, and you'll be fighting in the lap of luxury. Money money moneeey! ...MOOOONNNEEEYYY!

Greater Mark of Desolation: Makes your auto-attacks deal more damage.
Greater Seal of Armor: Combined with your regrowth pendant, resilience runes will reduce damage taken from AD champions as well as minions [on top of your passive].
Greater Glyph of Magic Resist: Ranged AP mages are your worst nightmare, so take thses to reduce their damage and regenerate a lot better with your regrowth pendant during the laning phase.
Greater Quintessence of Gold: This combined with all your other gold per time perks makes acquiring your items so much faster.

You need all the damage you can get to score kills during your roaming ganks, and rolling 21 Offense will grant that for you. The rest is in Utility primarily for the Greed +1, but also for the XP boost, death time reduction, and more hp/mana regen.

Mobility Boots Best boots for stealth in the game. Maximizes positioning for ganking enemy champs.

Wriggle's Lantern Minion proc's for more gold, gives you decent sustain, armor, and a free ward while you roam the jungle in search of enemy champions for ganking.

Trinity Force With all that gold you're making, the price of the Trinity Force is chump change for you. All the stats it gives you benefits you in all ways: damage, slow, attack speed, some crit., health to blend in with added defense later, and some mana to afford you a couple extra casts.

Infinity Edge Damage, crit. procs on top of your TF procs, and highest AD damage item in the game.

Note: Upon amassing enough gold for your Atma's and/or Banshee's, go ahead and sell your Philo Stone first, and then your Heart of Gold.

Atma's Impaler More crit to help proc your IE, and gives you added damage mitigation vs. AD damage to turn you into one beefy assassin.

Banshee's Veil One of the best defense items in the game. Blocks a spell every 45 seconds, gives you more health and magic resist to blend in with your other defensive stats, and your mana pool increases so you can use your skills more.

Other Items I would consider worthy of usage on Evelynn:

Guardian Angel A two-in-one defense compression item. Gives you both armor and magic resist to slow down damage dealt to you, and the Unique Passive can help you come back, stealth, and make an escape if you're lucky! It can potentially prevent you from getting killed, and consequently feeding enemies more free gold.

The current sequence reflects the path you should take when you don't yet have the Trinity Force. Upon buying the Trinity though, you should invest at least one (1) point in your Hate Spike (Q) so that you can proc your extra damage.

Smite Aids in pushing or preventing a push while in lane, give you 5 free gold per use to stack onto your already growing wealth, and enables you to steal all buffs while in stealth, including the most important buff: "Baron". Replacing this skill takes away from the goal of this build: make more money. Without it, you cannot steal dragon or baron so easily. I don't recommend going without it.

Ignite Prevents heals and sustain during ganks to help you secure kills better, and grants extra damage to boost Evelynn's DPS and help score kills. Replacing this skill takes away from your gank success, and I don't recommend going without it.

All other summoner spells just pale against these two. Sure, you can use other spells anyway, but I feel that you're gimping the success rate of this build if you do. If you decide to use other spells, then don't blame me and rate this build poorly because of it. Use this build exacttly as prescribed, play smartly, and you'll profit from it.

You'll want to Ctrl+G your targets and let your allies know who you want to gank. In team fights, you'll want to stay out of the scene, but close enough so that you can come in and take down squishies, or low health targets. NEVER INITIATE! Always let your tank or other allied champions do the initiating for you, and you simply finish them enemy champions off. So roam around the jungle, stay in bushes, and be on the lookout for easy prey.

Pro's:
Money Maker. You'll make tons of gold really, really fast, thereby gaining the advantage faster than most.
Stealth. You can force enemies to spend gold on vision wards and Oracles, get them killed while with Oracles, and set them back in items.

Con's:
Squishy. Can be killed easily if caught off guard.
Slow Starter. Damage is kind of small early game because Riot nerfed her into oblivion [go figure].

Please do not stray away from this build. Test it out, and tell me how it goes for you. If you have any suggestions, feel free to post them. You'll build items so fast the enemy team won't know what hit them!

Make that money, spend that cash, and buy your way to victory! Show those newbs that Evelynn can STILL own hard! GL and HF! :)