Blitzcrank is an all-round good champion that can build in to any type. In this build I am focusing to build him as a tank. Because of his grabbing ability he will often end up in close range fights and might often get focused being confused as squishy.

He is an exelent ganker and good at early-game kills. I play him tanky because I genrally use him mostly to help my team get kills and not going in duels.

Pros

Can build into anything
He litterally grabs free kills
Easy to escape with
Eats squishy for breackfast!

Cons

Grab is hard to master
Hard to deal much damage with basic attacks

Your items shouldn't be the same each game. It's all dependant on the enemy champions.

Always buy manamue!
These items are important to buy in different situations:
AD- Bloodthirstier
Tank- Thornmail/Force of Nature
AP- Rabbadons deathcap

The advantage of him building into whatever your team needs is extremely good. And his grab genally secures kills.

The skill sequence I have made is the one and only I would suggest. Always remember that Power Fist is your main source of damage. If you need to finish of an enemy, are in a team fight or need to push minions you can activate static field. Never use it on single targets with much health.