Id say , Skip Lich bane and Get Trinity force , and u dont rly need Clarity...

this is very poor. if you want a dps play tryndamere. dont even think about not building tri force on nasus.

I don't like how you have Lichbane. You say that it is a major upgrade to sheen when it really isn't for Nasus. Sheen and Trinity force increase your base attack damage where Lichbane goes off of your ability power. Your final base attack damage is 116 and your final ability power is only 80. You'd be missing a lot of extra attack damage if you get Lichbane instead of Trinity Force if that's the reason you are getting it.

On another note, if make sure to rush Warmogs first, before you even get sheen or level 2 boots, this build might be so bad. When I play him, I start with the regrowth pendant, then level 1 boots, then finish Warmogs, then finish boots and then sheen. About 80% of the time when I've finished my Trinity Force we have a significant lead. If played right you're pretty unkillable after Trinity Force. Then feel free to start getting dps items.

This build may work for you, but if I'm completely honest I have to say I think you've got it all wrong.

You mention that you started out playing Nasus with multiple Trinity Forces and then decided to alter your build because the Sheen proc is unique. Here's the catch: you only need 1 Trinity Force! What you are doing now is creating a build that is 5 times more expensive than simply buying Trinity Force without even having the Sheen proc that you really want to have until very late game when you build Lich Bane.

You mention that you should focus on farming your Q. This is correct, but it is also the reason why you don't need to build so many offensive items. Right now, you're trying to be an AD carry with a champion that is absolutely not designed to be an AD carry.
What makes Nasus unique is the fact that he can be very tanky while dealing loads of damage because the damage of his Q keeps increasing. You absolutely want to increase his Q damage by getting Sheen/Trinity Force, but once you get that item you should never, ever buy so many attacking items because it will only make you squishy while in fact you could also be tanky while still dealing a lot of damage. His lifesteal is great for your survivability but it only goes so far, with these items you will be squishy when you get focused. The masteries may be defensive but in my opinion that is more a rather laughable attempt to become less squishy.

Also, you really don't need Clarity. Clarity is a good spell to have when you're new to a champion and run out of mana often, but once you play a champion more often you should generally find a way to make better use of your mana or to solve your mana trouble in a different way (through items etc.). Also, his Q (the most important ability) only costs 40 mana on rank 5 so there is really no reason for Clarity.

I will not downvote because I think you deserve the chance to work on this, but there is a lot wrong with this build. I advise you to take a look at some of the higher rated Nasus builds and give them a try.