People run out of mana with Nasus because they like to spam Spirit Fire, which is a waste unless you're solo laning. Nasus doesn't need the extra survivability - that's the tanks job. He's good enough at surviving with his base stats, TF and Frozen Mallet. I don't know the exact increase in attack damage when you buy Atma's Impaler, but usually my AD goes from around 190 to well over 250. I think you'll agree that this is a very significant increase, and combined with the crit (on top of the crit from Trinity Force) Nasus' damage output goes up massively. The base cooldown on SS isn't high enough to be a problem, therefore I don't feel a Frozen Heart would be necessary at all.

This build is based mostly around playstyle anyway. To get it right you need to combine the item build with a conservative, farmy and tactical playstyle.

How do you absolve your mana problems as Nasus? Surely a Sheen by itself is not substantial enough to deal with all of them. Now here is my little piece of advice, you may choose not to pay much heed to it:

If you're taking too much damage, you can also substitute your Atma's for a Frozen Heart. Now I understand that you're wondering WHY you would sacrifice it, as they're completely different item types, right? But look a little deeper and you see the CDR and survivability. I personally have never seen Atma's being used well without a Warmog simply because most other individual items don't provide nearly as much HP as it, and you need item slots.

Until these things have been addressed, I'll abstain from voting.

Nice build !!!! =)