With this build you can play passive/reactive or aggressive/proactive.
It builds off Alistar's passive. This build gives a lot of sustain to your adc.

skill order.
Max out Q and E first because W is used to close in on someone but Q+E are to stick on them/cc allowing ur teams to put in the most damage possible.

Ardent so every time they heal from your passive they also receive life steal, AS, and damage.

you go locket to give your team a shield plus ardent passive + alistar gets armor/mr.

Gargoyle plate is to make up for the lack of health in this build.

knight's vow or zeke's convergence for preference.

Knight's vow gives health+cdr+armor. you get health for the damage they deal and redirect a portion of damage they take which works great for alistar when he's ulting. more defensive.

Zeke's convergence gives a huge boost of damage when he ults and add's a slow debuff to alistar allowing him to peel even when his abilities are on cd and allows him to stick on enemeis long enough to land his stun.

stoneborn pact for ardent.fearless for engages. recovery for passive healing in the back to engage again. runic for passive. tough skin for engages. bandit for gold. meditation for mana. wanderer for engages. swiftness to stick on champs.

you can also go windspeaker's and rely on locket/passive for full team ardent.

Expensive runes.
Life regen for poke if passive and healing up after engages if aggressive.
armor runes for AA's.
mana regen for late game low cdr abilities that well waste a lot of mana.
10% cdr for build which gives 30%.