1. Shoes of Magi - Necessary mobility and penetration in early game, makes Nu Wa hit really hard ( you can start with Mages Blessing if you have mana conserving issues)
2. Chronoa' Pendant - Rushing CDR on her is really important to have more ults throughout the match. MP5 is pleasant too
3. Spear of Desolation -Good source of power and penetration followed with additional necessary CDR to reach the soft cap ( we should stop at this moment, last 10% to cap 40 should be gained from mana buff or power potion)
4. Rod of Tahuti - Our main power spike, additional mana sustain and helpful passive to gain some kills with your ultimate (or any other skill :D)
5. Shaman's Ring - Another useful power item with good mobility addition to help us escape incoming threats. You prolly think thats crazy cause its too late to stack it. Dont worry, with power we already gathered stacking this is a matter of one good teamfight (and another 10% additional dmg to help us secure something with ult, or any other skill)
6. Obsidian Shard - We prolly reached late game, so tanks, warriors and other weak imbeciles propably built up some protections. This item will help us get through them easily
7. (Optional) Soul Reaver - If you really are upset cause of low mana pool, or simply dont like any of the items like Deso, Shaman or Obsidian i think Soul Reaver is a good replacement

Pfff, no special magic here. Usual Beads and Aegis to help us survive. Build order depends of what you want and when