I always use this build when im playing as Evelynn, I know that it's the complete oposite of what every other build is out there, but this ones better. i got 23/3/5 usng this build, sometimes even better results. This build is for 1v1 - 5v5.
Item 1: philophers Stone
Item 2: Berker's Greaves(gives tier 2 movement+25%attack speed)
Item 3: Phantom Dancer
Item 4: Infinity Edge(if ur lv 18, you'll be hitting constant crits of 430dmg)
Item 5: Malady(50% attack speed, 15% life steal)
Item 6: whatever you want, ur winning at this rate(Phantom Dancer is nice though
With these items at lv 18 u will have 93% crit chance
Use Malice and Spite with this build and you will "Own" them.