Should I do a camp level 1 as a top laner?

gromp if blue krugs if red

Depends entirely on whether the jungler is starting top side or bot side (don't take the camp if they are starting top side), at which point you determine if you can clear the camp quickly enough to not miss a bunch of minions, and if you can clear it without having to use any sustain (potions). Riven and Garen are already lane bullies/snowbally, so this could help them push ahead even harder, or if you don't take it quickly, you could very well end up setting yourself behind. It seems like taking a camp is better suited to a champ who is a lane bully (like how Sion does) and can also clear the camp very very quickly (like Maokai's sapling stack).