Hello everybody, and welcome to my first LoL guide. Now before we start I would like to go ahead and make note of 3 things.
1. I'm not a pro.
2. I'm not perfect and neither is this guide.
3. I did this guide as a little spare time project, so don't go crazy with the insults.

FAQ
Smite?
Since the Jungle rework it's been no secret that jungle has become an even harder carry than before (jungle mains rejoice) but sadly for top laners like myself this has just made it even harder to carry your team from the "island" that is top. However, how Riot went about reworking jungle has actually had an effect on solo lanes because smite is now an effective in lane spell. Rengar (along with any other champion that used ignite in top lane) has been buffed (indirectly) in top like crazy. Now you can get 20 armor penetration straight off the bat, instant ignite damage instead of an unreliable burn that also slows making Rengar even more of a menace in 1v1 situations.
I Thought Top Laners Had To Be Tanky?
Well, whilst top lane tanks used to be the Meta, this has recently changed (Lulu, Lissandra, Wukong), though people often stick to tank/bruisers with either hard CC (Maokai, Alistar, Malphite) or Tank-Damage output (Rumble, Pantheon, Garen) but with the new "jungle" items I believe assassins are now the strongest picks for solo top.

Pros

Great Sustain
High Damage
High Mobility
Push Potential

Cons

Squishy
Item Reliant
Over-Commiter
Mediocre Escape

Experiment with what you like and what fits best to your play style. I build Rengar's Runes/Masteries pretty standard, but I know things like Movespeed Quints and Health Seals work just fine with him. Along with that running 9/21/0 Masteries is actually really strong for early game in lane against squishier opponents.