Nasus's Jungle clear times are **** without Madreds.
Also consider the following:
Kindlegem and Glacial Shroud together cost 2200, and give you 20% CDR, 200hp, 45 armor, and 300 mana.
Spirit of the Ancient Golem costs 2100 and gives you: 10% CDR, 500hp, some regen and Tenacity.

Funny thing about tenacity though, most people won't spam their CC on you- you're the tank. If someone's using heavy CC on you, they're not using it on your adc.

The health and mana regen are basically wasted on him, especially with +300 mana. Then those two items then build into Frozen Heart and Spirit Visage.

The biggest problem is the health tradeoff; However all that armor and CDR is so worth.

For me, it seems like a pretty obvious choice. Bigger, better items, more armor, faster stacks.

If you're lucky, after your FH + SV are done, you can spend about 2 or 3 minutes stacking your q. you can easily gain 100+ stacks quickly if you fire it off every 4 seconds when it comes up. if you didn't sell your madreds and you have sheen, you can easily 1 shot most minions. If your team can stall for just a few minutes, you can emerge an unstoppable force.

Usually the enemy will try to stop you from farming your q. Be hyper aware of 3+ man ganks during this time. If they are, try to kite them in and have your teammates take objectives. Remember, You're suddenly really massive, and probably scarier than you realize.

Nasus is a melee chasing champ. By the time you buy trinity, you should have your whither maxed. with this, a 95% slow. And a q every 4 seconds. You can not only solo everyone in the game (except maybe kayle or a reeeeally fed mage), you're a teamfighting monster. Your q's should do nearly a thousand damage to a lightly armored target. That's a lot of damage! If you're somehow still getting blown up in teamfights, don't build a trinity. Obviously.

Nasus jungle should generally be reconsidered against a heavy AP comp. He has to get in close and all that magic can kite him around, especially without tenacity.

Building mercs instead of swiftness boots is obviously a priority. But what now?

Instead of building Trinity Force, build Frozen Mallet into Warmogs. Warmogs' passive stacks with the huge health boost from frozen mallet and your damage doesn't suffer too too much.

The downside is since you already have a 95% slow, the slow is a bit of a waste. If you're good at multitasking, you can wither the ADC and still put down a decent slow on another target by whacking them with your stick. However, stacking the two of them together won't really add anything noticeable. Build with caution.