Across 654 ranked games on patch 16.21 in Master and above, Sett mains win 53.7% of their games in the top lane.
Their most common build appears in 68.8% of those games and wins 54.2% of its 450 games.
It starts 
Doran's Blade and 
Health Potion, completes 
Stridebreaker, 
Black Cleaver, 
Overlord's Bloodmail, 
Sterak's Gage and 
Spear of Shojin in that order, and takes 
Plated Steelcaps.
Two other builds are played often enough in the top lane to be measured on their own.
In the top lane, Sett mains fare best against 
Ambessa (won 70.0% of 20 games), 
Darius (won 66.7% of 21 games) and 
Fiora (won 71.4% of 14 games).
Their hardest matchups, the champions that counter Sett, are 
Olaf (won 35.3% of 17 games), 
Renekton (won 40.0% of 20 games) and 
Singed (won 38.5% of 13 games).