Nashor's Tooth - It gives nice CDR, AP, and attack speed. It's a great item for Nasus. I just wish they hadn't removed the mana regen from it.
Trinity Force - It's expensive, the slow requires attack speed to be effective, and it needs AD for it's Sheen effect. It also has every stat Nasus needs as a hybrid and seeing pros using this in their streams while using Nasus top has made me reexamine how good it is for him.
The Black Cleaver - CDR, AD, Health, and Armor Shred that also helps the team. The Brutalizer is a nice early build piece granting some damage and some CDR.
Zhonya's Hourglass - High AP, Armor, save posterior special.
Rod of Ages - Health, Mana, AP.
Mercury Treads - MR, Movespeed, Tenacity, Homeguard
These have potential to me. It would just max out the 300 AP you need, max out CDR, plenty of attack speed, move speed, high health, some armor and MR, mana for sustain, a Sheen effect, a Slow effect, armor shred, even a little critical chance in case you feel lucky. Hourglass on use.
But what order do you put them in and would it be better to build some of the base items early: Seeker's Armguard is great for the price. So is Brutalizer. Stinger isn't bad either. Catalyst would be needed early to slow OOM. You obviously need Boots early. Getting Nashor's Tooth early means faster Q farming but will mana be an issue with faster Qs. That's the part that is troubling me. If you do it wrong, your early game suffers and you don't get a late game. Delay CDR too long and you will stunt the growth of your Q farm.
Thus more testing. My current test is running items in this order: Rod of Ages, Boots when necessary, Trinity Force, Nashor's Tooth, Zhonya's Hourglass, The Black Cleaver. Also switching runes to Hybrid Penetration instead of magical shows an increase in DPS. Which makes sense in a hybrid build. You won't be a major tank but you won't be squishy either. I would love to lead with Nashor's Tooth but mana becomes an issue. If Rod wasn't necessary, I'd prefer Liandry's Torment. A little squishier but the damage would be great on the AoEs.
Thus more testing. Ideas welcome.