I don't think you are right when you say "its not karma's job to carry especially late in the game" because the force of Karma is to be able to support your team in the early and to make damage while tanking in late game. But I admit than you can't deal as damage as Brand or Arhi but Karma have good ratios (especially on shield) and it's too bad not to profit from it.
Zhonya is not a good choice. why do I think that ? Just because
-if you also take Randuin you will have lots of armor whereas you should make HP or magic resist to balance (but i speak in case the opponent team is balanced too)
-replace Randuin by zhonya will give you an ap bonus what is really good but that item doesn't suit to Karma's role because zhonya's passive enable you to be sage during a few second. now karma isn't a strong carry then she isn't the main focus then she doesn't need that kind of protection. It's better to take randuin with a view to support your team: because if you become focused by the opponent ad carry you will decrease his attack speed and movement then you will not be focused if the other team thought a bit about it. Moreover, you can also decrease the attack speed by activating the item's active that help your team more than if you did a few damage more.

Rylai is good but karma has already a slow and with randuin's active you can slow too then it is not necessary because randuin and rod of Ages already gives you a lot of health.

Abyssal scepter is a very good choice too and you can replace lich bane with it because it remove a bit magic resist among the ennemis but I think i can be really efficient only if your team make lots of magic damage (at least composed by an ap jungler or solo top in addition to the main ap carry and you) or otherwise if the main ap carry is fed and it can be great to help him in order to face to magic resist the ennemies will make.

I thought lich bane was a good choice but I don't think you can get it before the end of the game because others items are more usefull. It just add more damage over time with short cd of Karma's spells but another item can be great too like abyssal scepter or warmog if you want to tank more and more. It's just necessary to look at the opponent team and if it is balanced or not. The last item need to be choiced according to the ennemy team. You need to adapt yourself.

I hope I helped you and perhaps made you change your opinion. Don't hesitate to explain your choices and to show why you think they are better for Karma.

You wait too long to get any AP in this build. Try getting a Kage's Pick. Also Keep your GP5 items until you can afford some AP items.

If you get some early Kills or assists you can get Rod of Aegis, otherwise get deathcap as you first AP item. There's also no need to get both Locked AND Randuin's Omen.

Its not Karma's Job to carry. Especially late in the game. Instead of Lichbane I'd recommend Abyssal Scepter, Zhonya's Hourglass, or Rylai's Crystal Scepter for some AP to boost your Supporting ability, and some durability with Mag resist/Health/armor.

Really Nice! i got 2 - 7 - 42

Okay build, could be better.

I loved it and it helped me... Good work

Thx, good build, even if I never managed to end it... I love "Locket of Iron Solari". Lich bane is very efficient cuz of Karma'cd...