2 Lifesteal Quints, 1 Arm Pen Quint, 8 AD Marks, 1 Arm Pen Mark, 9 Armor Seals, 8 Magic Resist Glyphs and 1 Armor Glyph.
Go 21/9/0 with these masteries; http://gyazo.com/f94ea36eb41cf9b9548d856e12a509bd
Or go whatever you want to. (^^Thats the recommended Zed for both Mid & Top masteries^^)
Starting Items: Always start with either Dorans Blade or Dorans Shield. Start Dorans Blade if you're up against some squishy Mid/Top laner. If you're up against some half-beefy champion, you can start Dorans Blade as well. If you're up against someone like Orianna, always start with Dorans Shield. Her Passive makes her Basic attacks hurt like hell. Or you know, a sunburn.
If you're up against someone like Yasuo, Darius or Renekton (Yasuo being both Mid & Top champion), for the sake of your impact in the game, start with cloth armor. They don't auto attack you as much as other champions, so having flat armor helps vs their raw phyical damage. And the 5 health potions help.
First Home: You should have around 1400 Gold on your first home, at that point you can choose Brutalizer or a Cutlass. Cutlass is for a more sustained lane vs heavy pokers and Brutalizer is more of a offensive choice early to outtrade your lane opponent with the armor pen (+runes).
First Item: It should always be a Blade of the Ruined King. No matter who you are, how good you are with Zed, ALWAYS BorTK since it synergizes well with his burst and ult combo.
Second Item: Get a Last Whisper ASAP after BorTK since again, it helps with your burst.
Third Item: This is where it gets tricky, remember that Brutalizer you've had for 15 minutes? Yeah, this is where their team depends on your following item. If you're up against some really beefy tanky top laner/jungler, let it be a Nasus, Mundo, Renekton, Jax, etc. I'll recommend you go Ghostblade. It synergize really well with your burst vs Armor stackers since you'll get 10 extra armor pen (compared to black clever) and the more attack speed = the more BotRK passive basic attack you'll get off.
Black Clever: This is the go to item if they dont have as listen above, a super tank. I know the armor shred would help a lot vs armor stackers like Mundo, Nasus and Renekton, but just from experience, I can confirm this item is better for snowballing from mid to late.
Fourth and fifth Item: This is where you start to build defensive items such as Maw, Banshees, GA and Randuins. If you're really ballsy and think you can 1vTheWorld, build hydra for extra burst. If you're a smart player, build Randuins and Maw. It gives you the beefyness you need and you still have a lot of raw damage. (Plus Maws shield)
Pros / Cons
Pros: You got a really strong early and mid game, abuse that. Do NOT use your w every time its up to harass, mainly use it when you know the enemy jungler is not close to your lane.
Cons: You start to fall off late game, a lot. This is why Zed is a high risk high reward pick, when late game comes, you, Zed, start to split push. Picking Zed is all about a split push team comp. I list this as a Con since Zed is a mobile Assassin, being able to literally 1 shot everyone.
There's a little trick with Zed, when you use your harass combo; W > E > Q --- When using this combo, as your W is shooting out, press E and it will do damage a split second before your W is placed on the ground. Zed is a really good farmer, so getting last whisper early helps a lot. Whenever your lane opponent is not there, farm wraiths. Also, for the early game; the reason behind the two lifesteal quints is because it synergize with your passive.