Nasus is considered a tanky champ. He's known for being able to solo towers late game. I believe I have come up with a build that not only gets him really tanky but also gives him everything else too.
Siphon is literally the best late game skill ever. max it out ASAP. sometimes i dont get wither until after I get my r if u love to gank wither is necesary. they'll just slow u and then run. spirit fire is good for minions and monsters, but in a tight situation the beginning dmg will kill a low health champ fury gives u a ton more HP and AoE dmg. good for tanky champs, because it deals dmg based on your HP