Across 1,618 ranked games on patch 16.21 in Master and above, Gangplank mains win 53.4% of their games in the top lane.
Their most common build appears in 59.8% of those games and wins 53.2% of its 968 games.
It starts 
Doran's Blade and 
Health Potion, completes 
Essence Reaver, 
Immortal Shieldbow, 
Infinity Edge and 
Lord Dominik's Regards in that order, and takes 
Plated Steelcaps.
Three other builds are played often enough in the top lane to be measured on their own.
In the top lane, Gangplank mains fare best against 
Singed (won 78.6% of 14 games), 
Sion (won 67.9% of 28 games) and 
Akali (won 75.0% of 12 games).
Their hardest matchups, the champions that counter Gangplank, are 
Aatrox (won 44.7% of 47 games), 
Garen (won 38.1% of 21 games) and 
Ambessa (won 42.4% of 33 games).