baaaaaaaaaaaad build, you will just be ignored because you don't do jack

Your skill priority for initiating a teamfight WTF? Wither last? Use Wither first to catch a squishy offguard. No Triforce - Bad. you do 0 dmg except if you got about +1000 dmg on your q and 20 kills. Rework it plz!

Grate! :)

no triforce and heavy on armor which nasus is already strong against because of wither

Uhm, I will not vote, because I'm really confused here, if you don't know that the common way of asking for a specific aspect of the game to be "debuffed" is to be "nerfed", we already have a veeeeeery big problem with your title xD

But if you were trying to be different, very nice catch :P

Anyways, your build is solid armor only, which is VERY dangerous, you do say to grab a FoN if they're AP heavy, but it's not like you ALWAYS run into AD heavy teams, dude.

I'd say:

List items to counter APers, ADers and Balanced teams
Get some COLOR >.<
Please speficy what kind of role you're trying to play (solo top offtank? duo bottom as tank?)
In fact, without a trinity force, you WILL have some problems with Nasus, as stated in one of the comments above.

Thank you for the comments.
And it's my first guide so I'll try adding some pictures.
Also simply telling me it's "Nerf" rather than "Debuff" isn't helpful at all.

Man, you got very little damage, and no MR at all, you will get owned by mages, and you won't be dropping anyone. Seriously, this needs much more thought.

Nasus, without a triforce isn't a nasus at all!

Debuff? its called Nerf...

Could need more pictures and text. Your rune and item choices are weird since you have health runes and you're already building a ton of health but getting Warmog's Armor REALLY late to be able to farm it up for Atma's Impaler. There isn't any MR items either for defense. I think you should add a bit more