I main Evelynn, feel free to look me up on LoLKing for my ranked stats, I've played her for over a year now, just started playing ranked with her since buff.
I stopped buying Wriggles on her. Sheen clears the jungle fast enough, and helps you do more damage where it counts: Ganks.
I never buy Phantom Dancer on Eve. It just does not help her, she moves more than fast enough and with her E she's nearly 2.0 attack speed for that time. If I do buy an A/S Item its usually bloodrazor or wits end.
In fact, if you want my advice I usually go two ways depending on my team.
Boots + 3 pots.
Boots of Mobility or Boots of Swiftness if people are just getting away. Its rare, but I do notice it helps in those situations.
Infinity Edge or Blood Thurster(I will get a BT if I'm being more farm oriented and not getting a lot of ganks, IE if I'm getting kills.)
Gaurdian Angel - > At this point, team fights are starting. You're GOING to get focused. Make them regret focusing you.
Finish Trinity - > I wait this long because IE/BT Does more damage than the 50% and GA is needed. Sheen gives you absurd damage alone.
At this point everything is situational. IF you are stuck on PD, you could get one now. I normally build IE if I haven't or BT if I haven't. If they are AP heavy I'll build a Maw of Malmortius and Wits end, If they are AD Heavy I'll build a Thornmail and Bloodrazor.
Your Q and E have GREAT scaling for AD/AP, its almost always better to build damage over attack speed on Evelynn.
Boots + 3 pots
Heart of Gold(I know you're saying you should buy this first. DON'T! Sheen adds so much damage that you need it to gank. Really, listen to me.)
Guardian Angel(What? Already? I know, trust me you do a crapton of damage with sheen and GA will make you invincible this early.)
Turn your HoG into a Randiun's and USE it after you ult and run into a group. You will take nearly no damage, and no one will be able to run for quite some time.
At this point if you're damage is lacking, finish your trinity, if not build accordingly. I usually go for an Aegis of the Legion for all around defense/hp.
If they have a lot of AP, I'd go for Maw of Malmortius or Wit's End.
If they are AD Heavy, Thornmail and Frozen Mallet should do you well.
My last item I will almost always go for more damage, because at this point you might need it. Grab a BloodThurster or Hextech gunblade. The sustain and damage from both will be awesome. You can even build it sooner if you feel you're just taking enemy hits.
Usually you'll never finish a build with Evelynn, but if you get into late game you will be doing serious damage. She's very farm and kill hungry, and item dependent. Remember to be patient, because you will always have a great late game if you play her well.