Across 1,499 ranked games on patch 16.21 in Master and above, Jayce mains win 48.0% of their games in the top lane.
Their most common build appears in 28.7% of those games and wins 51.2% of its 430 games.
It starts 
Doran's Blade and 
Health Potion, completes 
Youmuu's Ghostblade, 
Manamune and 
Voltaic Cyclosword in that order, and takes 
Ionian Boots of Lucidity.
Three other builds are played often enough in the top lane to be measured on their own.
In the top lane, Jayce mains fare best against 
Ambessa (won 70.0% of 30 games), 
Kled (won 73.3% of 15 games) and 
Yorick (won 63.6% of 33 games).
Their hardest matchups, the champions that counter Jayce, are 
Ornn (won 16.7% of 12 games), 
Sion (won 30.0% of 40 games) and 
Olaf (won 38.5% of 39 games).