Good summoner Spells:
Ignite: Finish off kills and heal reduction
Ghost: is awesome my favorite summoner spell
Flash: the Ghost flash Combo is pretty OP
Cleanse: good for those teams with lots of stuns or taunts or slows.
Exaust: Slows and reduces dmg witch is very nice too be like wither then exaust hahahaha infinite slow...
Secondary summoner spells:
Teleport: sometimes i just like being that guy to **** block people trying to push towers or just get back to lane asap to farm more.
Fortify: Isn't bad the passive is decent also again another **** block.
Clairvoyance: ITS OP lol just a nice free sight on enemys nice sometimes.
Summoner spells i stay away from:
Revive: The CD too long sometimes its fun to troll and put revive with teleport lol
Heal: One of those summoner spells that will make difference of getting killed or getting a kill early game but just early game late game its a waste of a summoner spell
Smite: Unless u be jungling nasus dont take this lol.
Clarity: if your not using MP5 runes sometimes nice again only early game late game not really gonna make a difference.
Primary: Armor Pen Marks, HP per LvL seals, Flat CDR Blues and Flat HP quins.
Secondary: MP5 per level Yellows are nice helps u stay in lane longer to farm, CDR quins are nice too so u can Siphon Strike spam some more, MP5 per level Blues(Glyphs) also nice if you combine them with MP5 per lvl yellows you will never have to leave a lane due to mana issues.
My Rune Page:
Randuin's Omen: Has good armor HP good chance when being hit slow and and active that slows movement and attack speed.
Trinity Force:The extra dmg u get when you use an ability the movement speed and attack speed chance on hit to slow them and the HP Very awesome item.
Force of Nature:Awesome HP regen and Lots of magic resist
Atma's Impaler: Good armor with Crit chance and the decent amount of atk damage u get.
Aegis: Is just an awesome tank/support items armor hp MR has everything u need.
Starks: Good atk speed Lifesteal regen its all around nice item.
Hexdrinker:Become a HUGE fan of this item when it comes to certain teams its very cheap depending on their makeup this is a very good item to get with the MR atk damage and 300 magic dmg it absorbs
Gaurdian Angel:Like i said in some of my other builds the nerf to this item to me kinda makes it useless.
Banshee's Veil:Is very situational if there is lots of magic dmg i would get this in place of the randuin's.
Early Game: Grab Doran's Shield and a HP pot, Try to get a solo Lane if you get mid by lvl 4 you should be going between Minion Waves the the Wraiths just for that little bit of extra XP and to get your Q stacked. The trick to nasus is getting those last hits with Siphoning Strike you must get those last hits with Siphoning Strike to keep your Q hitting hard. Go back when you have enough for at least your Tier 1 Boots and a Heart of gold. By level 6 you can go solo dragon.
Mid Game: By now you should have your Randuin's Omen and your sheen go back when you have enough for your Phage then try to stay in lane and gank until you have enough for Trinity Force.
Late game: If going right you should have your Trinity Force and your Force of Nature by this time in the game your Siphoning Strike with the Trinity Force you will be hitting for over 600 and critting easily over 1k. By this time the game is done but if not work on your atma's then you will be hitting even harder. If you they dont have much Spell dmg pick up a starks instead of a force of nature for extra atk speed and lifesteal also some hp regen its a nice item
With this build not only are you very tanky with the High armor MR and hp you will have but with your ulti poped you will be hitting much harder and have even more HP. What you want to do when going in for kill is Wither, Spirit Fire to reduce there armor and spam Siphoning strike... Take note That Siphoning Strike works on towers so Nasus is an excellent tower killer.
Keep In mind to get Red Elixers if you have that extra Gold Elixers make big differences in games..