I start with a dorans ring because it really fills everything karma needs. Next I go for CDR boots because it's important to get max CDR fast on her. More CDR = more heals and better farming with her shield. After I finish the boots I head to Morellos tome. Great item for Karma. Gives her MP5 to spam spells and also more CDR and ap. I just find the item too good to not get. Now your CDR is maxed. Let the spamming of mantra begin. After I build my tome I try to lane long enough for my Needlessly Large Rod. A lot of ap for the bigger shielding and healing. After that is complete I complete my Rabadons Deathcap. That is the core build. After the core is complete i'll either head to Zhonyas Hourglass if there is a lot of physical dmg. If they have more ap than physical I will get an Abysal Scepter. Great item also, gives the aura for the team and gives you more defense. Most likely they will target you because they wont be able to kill anyone lol. So if you get Hourglass first I would get Abysal next and the other way around. From there on out it is your choice of what to get. Do you need more defense? Or are you dominating and can get more ap. Personally I stack ap just because the more ap you have the bigger heal and more defense you have anyways with the shield. Plus more ap helps with Rabadons.