Across 747 ranked games on patch 16.21 in Master and above, Riven mains win 53.7% of their games in the top lane.
Their most common build appears in 26.0% of those games and wins 54.1% of its 194 games.
It starts 
Doran's Blade and 
Health Potion, completes 
Axiom Arc, 
Endless Hunger, 
Death's Dance and 
Maw of Malmortius 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, Riven mains fare best against 
Tryndamere (won 75.0% of 12 games), 
Jax (won 68.8% of 16 games) and 
Ornn (won 72.7% of 11 games).
Their hardest matchups, the champions that counter Riven, are 
Olaf (won 38.9% of 18 games), 
Fiora (won 38.9% of 18 games) and 
Renekton (won 45.8% of 24 games).