Here is the karma build, which is for me the best one. Why? Cuz u will have good defensive stats and your support spells will be also rly usefull. (sry for my bad english)

All u need to be good farmer are your CD reduction boots Q and E spell. U can farm only with Q spell, but on start i recommend this combo: Mantra-E,Q, whic will deal heavy dmg.

Items are standart support from the start. Late u will need also some damage so u will build scepter and dethfire cuz its active ability is great for Karma, who doesnt deal so much damage.

For summoner spell i use clarity, cuz on start i get life crystal so my mana split in sec. Flash is standart for champs like Karma i think just for good escaping.

My Karma as u can see is almost based on absorb thats cuz it was buffed :-D and its really usefull. her all abilities are great support but u have to fokus on 1 to be good supporter.

When u have runes like me and u get from start life crystal your enemies will not even try to kill u with ur huge HPs :-).