x9 Greater Mark of Resilience (+0.91 Armor)
x9 Greater Glyph of Warding (+1.34 Magic Resist)
x9 Greater Seal of Resilience (+1.41 Armor)
x3 Greater Quintessence of Warding (+4 Magic Resist)

I choose these mainly because it makes being a tank/harass early game amazing.

Defense: 26
Utility: 4

With the extra bonuses chosen, it just makes tanking early on easier.

You'll want to take a point in Rocket Grab at the beginning of each game (obviously). Then take a point in Powerfist at level 2. And picking up Overdrive at level 3.
Get your ult at level 6, 11, and 16.

Basically after you have 1 of each skill you can honestly focus on whatever order you want to, but I reccomend maxing out overdrive as fast as you can to give you that extra mobility.

Master Powerfist last because you only need the 1 point for the extra stun.

Flash: For the obvious escape/catching ability and flash+rocketgrab combo.
Ghost: For the extra mobility.

Pick up a Sapphire crystal and 2 health potions as soon as the game starts.
The more mana you have at the beginning, the more shield bonus you get from your passive champion skill when you fall below 20% health.
Picking Sheen early on gives you that extra damage bonus considering you're gonna be using your skills a lot. If you use Sheen properly, you can deal some decent damage with Powerfist.

All these items focus on Blitzcrank tanking early game and then focuses more on harassing with a damage bonus for late game.

Pros: You'll be an amazing tank/harass and people will fear you
You can catch up to your group and help tank/harass a.s.a.p.

Cons: You wont get many kills late game
If the people fear you too much, there wont be much action and the game may get boring