This are the basics.But if you have an opponent like fiora or garen you can take exhaust instead of ignite or even flash.You can also take ghost in the place of flash

You can take infinity edge as 3rd item instead of frozen if you see that you dont die easily.Bloodthirster also could be a good choice at first so you can stay up to lane especially if you wanna farm more than your opponent.
The last whisper is the perfect choice for anti-tank.I think you have noticed that i dont have bonetooth necklace on my build.Bonetooth Neclace is not a good item for rengar cause it dont provides extra damage (i dont mean the damage per level i mean in general like the other items).The only good of bonetooth neclace is that it gives armor pen and movement speed but its difficult to fill it especially when you are a ''feeder'' and dive in teamfights first or go all time solo and they kill you.But if someone wants to pick bonetooth i advice him to pick it at 20-35 because this is the time where all teamfights happen.