This is my first build here, so any constructive criticism is appreciated.

I plan on keeping this build as simple as possible. This is a pure support build, so you will need a laning partner who can do some damage (read: AD carry). The three main concepts of this build are:

Using Runes/Masteries to get 20% CDR
Building Lots of AP
Get Starcall When Team Fights Start

All CDR items come with 10/15/20% CDR on them. By getting 20% CDR with runes, you eliminate the need to get more than one CDR item. I usually run with Morello's for the nice amount of AP and MP5 it gives.

If you like using 2 or more CDR items, make sure you don't rune too much into CDR. Remember that CDR is additive an has a hard cap at 40%. Note: The 31.1% CDR does not take the 6+3% from masteries, which cause it to hit the CDR cap.

Example:
Lf you run with Boots of Lucidity and a Kindlegem, only use runes (and masteries) to get 15% CDR.

6% CDR from Intelligence (support tree)
3% CDR from Sorcery (attack tree)
No more than 6% CDR with runes

Is pretty straight forward. Here are a few items I like to get:

Morello's - CDR and AP
Rod of Ages - AP, health, mana
Rabadon's - Straight up AP
Rylai's - 15% slow if Starcall hits the bad guys, get it when team fights start

Rylai's + lower MR for you team = great supporting spell in team fights.

I hope this has been a fairly straight forward guide. I really didn't want to go into detail about all the choices I made, so if you have a question or comment on how to improve this build, please let me know!