Hello!
It's my second build :)
First: The items

At the begining Doran's ring is good for the Ap+ a heal pot for your life.
Then shoes, and more Ap. Very important is cooldown reduction, too.
At the end of the game you sell the ring for Zhonya's Hourglass.

Second: The skills

You skill the cage for..right, cage your enemies. Then your slow, which is like a bomb..use it like this if you want to attack. Then the shield for your mates and yourself. You skill always this both skills and your ulti for good dmg and to be safe.

Third: How to play

At the begining of the game you should be careful. Your damage is low like your life. So play defensive and hope for good lane-mates.
It get better in mid and end game, but you can't fight alone against 3 or 4.
You should try to slow first, than cage, let your slow explode and if the enemy have not much life use your ulti and kill them. If your team-mates want to kill you could use your ulti early or at first..but do it just, if your team is really secure to kill him.

Fourth: HAVE FUN !!