Weird, considering yes, rushing an item is great, unless your like against riven where you pretty much have to build iceborn, it allows you to figure out if you will go trinity, iceborn, frozen heart, if you need mr, etc. The big thing about nasus I find, is most people don't realize that his two strongest items, are trinity and spirit visage, once you have those 2 items, you are literally a handful for ANYBODY (Fk you trundle, I am not including you, fk you trundle).
There are a lot champions that fall into this category, I will name 3: nasus (trinity, visage), olaf (tabi's, visage, BC), Trundle (visage). With enough kite, these champs can be dealt with, but ALL 3 of them have the ability to slow/stop your kite, trundles pillar, nasus infinite slow, olafs Q, ult speed boost.
My personal favourite is this using the grasp of the dying, with the tenacity mastery, etc etc, secondary masteries are AS, heal after kill, lifesteal/vamp, dmg+ on slow.
Use a 10 cd rune page (This is a fucking expensive rune page I am about to tell you to try to get, lol),
All level 3 runes, 3 flat cd quints, 3 flat cd glyphs, 6 mr glyphs, 9 armour seals (Or health, I use health if I know I am likely to go iceborn, but armour if I am going trinity), and 9 AD marks.
So: 10 cd, 8.5 damage, 8 mr, 9 armour.
The thing about this is, I will rush sheen, and then after that, spirit visage. The reason being that spirit visage gives you soo much more heal on your passive, Q, and if your using the 2% lifesteal/vamp mastery, with your ult, E, and Q'ing, using the 8% all heal increase mastery, with grasp of the dying, this is what gives nasus those intense heals. Even grievious will have trouble here (ask f**king trundle, he will tell you all about it)
People like to go Tlords for the 5% xtra cd, I would not recommend as tlords will not scale in any way for nasus.
Another thing I have noticed is that nasus doesn't seemed to be played a lot atm, due to either being directly countered by trundle, or a huge simple fact that no nasus seems to realize that your E is FUCKING SUPER OP, if you are stacking good early and are able to rush sheen, Q'ing an enemy in E will do literally 2/3 more damage, unless its a thronmail malphite.