I dont play nasus on my main but I do dabble with him on my smurf account, Im not going to rate this guide as Ive never played with this build but I would suggest you try playing Nasus and maxing Spirit fire> Wither> Siphoning strike, 1 point is all thats needed in siphoning strike, all the damage is going to come from kills with it, and I also always pick up Sheen and Trinity Force even when tanking. Also for Runes instead of flat mana, try Mana per 5, it helps alot more, and if your going to actually go hardcore tank with nasus like your gear shows you might want to use more defensive runes instead of attack damage runes.

Any criticism will be appreciated. Thanks peepz