I and my Friend came to the same Build idea and tested succesful
The Build for HalfTank ap (because all other ways to play him i sucked)
(sry for my bad english)

Pros:
-high life and normal def at start
-Good dmg if u have Lich Bane
-Mostly alived in Teamfights
-can hold an enemy in teamfight with ulti
-Ulti low cooldown if u attack mana golem or so
-Spammable Skill
-with many Cooldown and good deff and HP your shield can hold full 6 secs
-good harrasment

Cons:
-Low mana at Start
-Shield skills breaks fast if isnt lvl 5
-E skill 2. effect is hard to become by minions

Q Spells as First because u can spamm it on Minions and other enemys

W Skill as 2. because u should enough life and def to hold the shield and + 2 or more hits on champion and the shield should be rdy fast enough

E Skill as last because the 2. effect cant u use on minions because they should be death already before u can use it again

Your Ulti + GHOST = IMBA ... is awesome in teamfights
or tower diving u can hold a champion in teamfights while your team attack him or the others to win the fight
or to take the enemy in your tower range ^^
or use to take the enemy from the tower to attack him with your lane partner

After you have Rod of Ages you should so how your enemy team is:
Rabadon's Deathcap or for Mage Abyssal Scepter or for Attack dmg Zhonya's Housglass

You can take the items in a other way but you NEED LICH BANE

My Gank idea (hope no one use it to me :S)
If you want to gank then speak to the team wich u want to attack then use your ghost and your shield and use your ulti to take the enemy to your team so fast you can

In Teamfihgts take your ulti to hold a champion they has low hp or hold the champion they make alot of dmg how Annie or others how tryndamere to def your team for a short time