This build is a safe high damage Rengar build. With the new reworked jungle and items, the only damaging items that you will need is the Warrior enchantment for your jungle item and Youmoo's ghostblade. You will have around 200 AD late game and enough armor pen and CDR to shred carries and get your ult off more than enough times than you should need. The reason for picking up a randuins omen is because you will have enough damage already as I said earlier, and to be relevant in teamfights you need to be tanky for engaging. This provides enough HP and armor to protect yourself against heavy AD teams. You do not need to pick up a Spirit Visage but I would prefer it if the enemies do not have a poke heavy AP team. This provides you with more HP and a lot of CDR for your ult and not to mention the passive is really great on Rengar considering he has a really strong self heal with his max ferocity stacked W. Guardian's Angel is not mandatory but it really helps late game in teamfights. Any item will do for your last however. Your choice :)