I got told awhile ago by someone else who supposedly mains Kayle that my AP/AS is weak compared to flat AD. But, the build I use has worked pretty good with little editing around all the recent changes to items/masteries. I currently don't have my client logged in so I am unable to look at my masteries, but they're very heavy offense (I even have an experimental all offensive page).
The items I start with are a ring and boots. Ring for a little meat early game, some early AP to splash around, and the mana regen while a little unnecessary is nice. From there I go berserker's, malady, nashor's, rageblade, gunblade.
At this point its up to interpretation of the match. I used to go Black Cleaver to further shred armor on top of my passive, get a little more AD, and just keep stacking AS. While my build lets me deal insane damage, and the AP gives my heal a nice boost too, I lately sell the ring and swap it with a Ruined King. Its even more life steal, a bulk lifesteal active, and more attack damage. I find the armor shred is really unnecessary when you're already shredding armor/magic resist so much that your AS/AP tears people up.
Finally if the game goes on long enough to reach this point, I sell my greaves for a Trinity. More meat, a constant slow (while there is only a % it will work, you land so many hits it might as well be 100% success), steroid from Sheen, and the speeds from Zeal.
As for skills, I go start E, and alternate with Q until I get the ulti, and don't usually take the heal til mid game. I play fairly passive vs enemy champs early and just bully people E while farming (love the splash)