Nigma isnt needed for doing ubers as trist is rather small, you *MIGHT* want one if you are going totally solo to find lillth and izzy but then you get into needing fcr to be effective. Otherwise stick with coh the 2 skills and resists will help you tons more than anything nigma has to offer for doing uber trist.
Shako --- good for life/mana
Gores --- Crushing blow
Dracs --- Life Tap
Coh --- Use this, doesnt have to be a AP, any coh is fine.
Tgods -- Id go with dungos instead
Raven -- That or a BK
Dwarf -- Raven or BK, dwarf not needed IMO
Curio -- Try for a seraphs even a +2/+1 pretty cheap
Exile -- Highly reccomended, can be done with others but by far the best.
Weap -- I prefer last wish over grief for life tap and cb but if you can't
afford either find a 3os mace with some mods and put the "black" runeword
in it, for an uber cheap cb weapon.
Skills:
His build is great, although I would reccomend using a couple spare points in salvation to combat meph's conviction. I normally go in (bo if you can) turn on salvation, then head right to meph. He goes down ez and the other 2 surround you, once hes dead switch to fanat and take out the other two. With them all surrounding you you should have plenty of life tap firing off keeping your health nice and high.
Just beware of bone prison and wraiths, nothing worse than killing everything around you finding yourself trapped inside a bone prison then getting killed by ranged attacks before you can break out!