The Zilean build for Support is Shurelya's Battlesong and Summon Aery. This LoL Zilean guide for Support at Platinum+ on 13.24 includes runes, items, skill order, and counters.
Zilean Counters
51.8%
(0.0%)
55.9%
(-0.6%)
2.4%
(+0.1%)
0.6%
(-0.1%)
349
(-8)