Across 1,793 ranked games on patch 16.21 in Master and above, Zed mains win 53.0% of their games in the mid lane.
Their most common build appears in 51.0% of those games and wins 55.6% of its 914 games.
It starts 
Doran's Blade and 
Health Potion, completes 
Voltaic Cyclosword, 
Bastionbreaker, 
Lord Dominik's Regards and 
Endless Hunger in that order, and takes 
Ionian Boots of Lucidity.
Three other builds are played often enough in the mid lane to be measured on their own.
In the mid lane, Zed mains fare best against 
Galio (won 67.9% of 28 games), 
Sylas (won 62.7% of 51 games) and 
Yone (won 57.4% of 54 games).
Their hardest matchups, the champions that counter Zed, are 
Vex (won 21.4% of 14 games), 
Lucian (won 20.0% of 10 games) and 
Locke (won 41.4% of 58 games).