Hey there, I have used a lot of the guides on mobafire, especially when i started out playing LoL and so thought it was time to give a little back. I like using Zilean as a support that can also dish a lot a fair amount of damage and i hope that you can try out this build and find it works as well for you as it does for me.

I usually take:

Flash - Because it has saved me countless times from ganks and also allowed me to flash in and throw down a Time Bomb on a fleeing enemy with minimal health catching the kill.

Clairvoyance - Because you're a Support and its damn useful for scouting, whether checking dragon/baron or for possible ganks in team fights.

With this build I aim for some bonus Ability Power and Magic Penetration in Offense, and then build towards Cooldown Reductions boosting my Mana Regen and Experience Gained in Utility. This really helps a lot and later in the game ur casts will be around 3secs for Rewind allowing you to spam Time Bomb and Time Warp.

Also another nifty trick i like to use is if who head back to base to buy an item or heal, spam Rewind to cooldown your ultimate allowing you to get it up instantly.

I start off with Ruby Crystal and aim to get Rod of Ages asap as it gives some nice AP as well as Health and Mana benefits that allow you to lane for longer early on which is always important.

Next i build up Ionian Boots. At this stage of the game its important to have some good movement speed for catching fleeing enemies with a double time bomb (Q,W,Q) and the 10% CDR is important for Zilean.

Next I take Rabadons Deathcap as it will give you that extra firepower that you will need to keep enemies wary of you and your partner, with Zileans massive range it usually allows you to dominate the lane and in teamfights allows you to dish some good damage in assisting with enemy Carry takedowns.

At this point i start aiming more for the defensive and support roles. Guardian Angel is basically a mimic of your ultimate, Chrono Shift, except its on a longer cooldown. This essentially makes it impoossible for you to lose in a 1v1. If they stick around after you recover using your ulti then do not fear, hit them with all you got...down you go again...only for them to QQ and shout all sorts of abuse at you as you revive once more to finish them off. Lets not forget though that as a support having Guardian Angel allows you to focus solely on supplying you teammates with Chrono Shift, which they will be more than grateful for and reviving important champs such as a Carry can seriously affect the outcome of any teamfight.

Frozen Heart is a great defensive item as it offers a further 20% CDR which makes ur casts seriously spammable and gives you another 500 Mana to make sure you can spam those casts for a lil while longer ^_^

Lastly i take Will of the Ancients which gives some nice bonus AP as well as spell vamp to both you and your team mates which is very useful in team fights.

PROS:

Kick *** beard!
Ultimate is ridiculously good and can turn the tide of a team fight
Good slow
Great Range

CONS:

Can be hard to farm at the begining
Pretty weak alone
Relies on 1 cast to deal damage

I hope you like my Build and find it useful. If not then please feel free to add any Critiques you like. I will keep this updated if any changes occur that should affect the build or Zilean in general.

Other than that, GL and HF