I'm just going to say a few things here.

"Rush to the damage dealer and-"

And get peeled off. Anyone with a brain will CC you. Then you get kited to hell because you're Nasus, and teamfight lost.

Overall, pretty questionable guide to put it nicely. Any Nasus player will tell you defensive masteries are much better than offensive, and ignite is completely counterproductive to Nasus's kit. In it's current form, -1 :(

I am not sure how you justify your choices for the offense tree for Nasus as he has only one skill that scales with AD which he can stack additively infinitely. Seeing as Nasus must farm it is really silly to trade defensive stats for offensive stats when your primary objective early is not to trade with enemy champs but to farm. Sacrificing beneficial stats like perseverance and second wind for say Executioner which gives a 5% more damage on a target below 50% health is far from worth it especially as Nasus will never chunk anyone down to that early game to make use of it unless by some miracle he gets a godly gank that succeeds. In the late game it could be very helpful but let’s be honest you won't make it without decent defensive stats and sustain. A Riven, Darius, Olaf or Yi will destroy you in a flat out duel that early or harass you faster than your passive can heal back for you.
Runes are fine, many I would trade for others but certainly viable. However many of your item choices are incredibly rare and situational on Nasus. Others I am sad to say are downright foolish. I am looking at you Athena's and Abysmal Scepter specifically. Sorry m8 but this build is not even close to optimal let alone viable.

It is a tad bit short.

Why not add in other viable summoner spells, like Teleport and Ignite?

What about alternative items? Situational items?

What about a section on his laning? His role in teamfights? Matchups?

Thank you, I'll definitely work on expanding it and making it less dull.

Very standard information :P

Add some summoner spell alternatives and a tactics section and it is worthy :P

Still a bit dull though, I would add something of an own style to it.

Something funny, something proffesional or something cute, I don't care ;P
Make it more interesting to read :D

Good luck
-Meiyjhe