I think a mana item is core on every build...ekko desperately needs mana regen. I usually use your first build but i build a morello instead of zhonyas
i think lacking mana/mana regen on a cdr build is a recipe for disaster. not to mention i don't personally agree nashors since there is a cd on his passive but it isn't bad
2. Morellonomicon, Ionian Boots of Lucidity, Luden's Tempest, Rabadon's Deathcap, Zhonya's Hourglass, Void Staff
3. Morellonomicon/ Rod of Ages, Sorcerer's Shoes, Abyssal Mask, Zhonya's Hourglass, Rabadon's Deathcap, Void Staff
Switch item orders based on need.
Lich Bane, Sorcerer's Shoes, Rabadon's Deathcap, Luden's Tempest, Zhonya's Hourglass, Void Staff.
CDR AP
Nashor's Tooth, Ionian Boots of Lucidity, Luden's Tempest, Rabadon's Deathcap, Void Staff, Zhonya's Hourglass.
Tanky AP
Rod of Ages, Mercury's Treads, Abyssal Mask, Zhonya's Hourglass, Rylai's Crystal Scepter (that e slow tho), Void Staff.
Joxuu's suggestions are probably better but these are my opinions (>^-^)>