Many people haven't been reading the last paragraph so I will put it in front... This is not finished since it takes time to write and post videos/pictures. I will be adding more but wanted some early feed back on what I have so far and some info on what people need to know about Nasus. All constructive comments are appreciated and once again, please don't dock the guide for lack of content quite yet. I would like to know any questions people have about Nasus and this guide. Thank you.

This guide is meant to serve as a thorough analysis of the champion Nasus. Don't Look at this as a build but as a template to jump off from.
A SIDE NOTE: The cheat sheet stats do not accurately reflect my suggested build. For some reason the stats from the mastery trees were not added in. This is most noticeable with the cool down reduction stat (2.39% at 18 with 1 Greater Quintessence of Celerity, 8.62% at 18 with 9 Greater Glyphs of Celerity, 4% with Sorcery mastery, 8.1% at 18 with Enlightenment mastery, and 15% with Shurelya's Reverie) 2.39+8.62+4+8.1+15=38.11
Another note is that when looking at rune stats, the numbers are often rounded and a user is unable to determine the exact value of the runes until they are placed in the rune page.

9 Greater Seals of Vitality: these runes provide one of the biggest bang for your buck in the game. Quintessence of the same nature are only about 2.5 times the strength, so these are considered a primary seal. Many people use armor or magic resist runes for their seals but I find that the amount of armor or magic resistance received is negligible if at 18 runes are chosen and plateau too quickly if flat bonuses are chosen. the Greater Seal of Vitality gives extra health early enough on that it can help with lane sustain, especially when coupled with a Regrowth Pendant and Nasus' passive life steal.

9 Greater Marks of Desolation: There are no primary marks that serve a purpose in a tank role, so these marks were chosen to amplify the damage of Nasus' primary attack, Siphoning Strike. An argument could be made that Greater Marks of Insight should be used, as they will increase the damage that his ult does, thus increasing his attack through the damage dealt by the ability. I would strongly suggest the armor penetration as it will aid in the last hitting of minions with Siphoning Strike.

9 Greater Glyphs of Celerity: Cool down reduction runes are one of the best in the game. Analysis of the amount of Cool down reduction provided by runes compared to items shows that items can provide a higher amount of any stat compared to runes but cool down runes match the amount given by the average cool down reduction item. Cool down reduction is essential to Nasus for three reasons; It allows him to farm his Siphoning Strike at a faster rate, It allows him to use Siphoning Strike more in a team fight since the cool down is shorter, and it allows his to almost continually have an opponent slowed by Whither.

1 Greater Quintessence of Celerity: This rune puts the user as close to the hard cap 40% cool down reduction as possible. This is for the same reasons previously mentioned.

2 Greater Quintessence of Desolation: These runes are chosen for the same reason as the marks since they greatly affect Nasus' early ability to last hit.

In the mastery trees I went for cool down reduction and PvP survive-ability. I spent points for the following reasons: 1 point in summoner's wrath to increase the effectiveness of ghost, 3 points in Brute force to aid in stacking Siphoning Strike, 4 points in Sorcery to lower cool down for the same reasons I have mentioned before, 3 points in Resistance to improve early magic resistance for sustainability, 3 points in Hardiness to improve early armor for sustain-ability, 4 points in Durability for a small health boost that improves as the the game progresses, 3 points in Vigor to improve sustainability early on, 1 point in Veteran's Scars for an early and effective boost of health, 3 points in Enlightenment to maximize cool down reduction, 3 points in Honor Guard to improve sustainability that lasts the entire game, 1 point in Juggernaut for a boost of health and an impressive 10% boost to tenacity, and finally 1 point in Summoner's Insight to lower the cool down on Flash.

This sequence is to maximize Siphoning Strike stacks and provide a defense to counter aggressive opponents while also improving the ability of other friendly champions to gank the lane Nasus holds. This also pushes back the purchasing of Spirit Fire, which is a very costly and ineffective spell. Spirit Fire should never be used during the lane phase as it pushes minions to an indefensible distance from your tower and will quickly drain your mana.

I'm a huge fan of getting into and out of fights quickly to take advantage of numbers or position so Flash and Ghost are personal favorites and they prove very effective when others use them too. For many people who have issues timing these spells or get in over their head too often Flash and Exhaust are a good combination, but I find exhaust to be a redundancy of Whither and with my suggested skill sequence and max cool down reduction it has less than a 7 second cool down so you should always have a whither ready.

A Regrowth Pendant and Health pot start coupled with Nasus' passive Life Steal and the increased health pool this build gives with keep you in lane for as long as you need.

It is however a good idea to return to base at a couple key gold levels regardless of health or mana. At 715 gold you have enough to return to base and purchase a Philosopher's Stone and Boots of Speed, this is a good option because it will help with escapes, chases, last hitting, lane sustain, and you get a gold bonus that doesn't hurt.

You can also hold out until you have 1260 gold and return to purchase an early sheen and get your boots and Philosopher's stone on your next trip, but I would avoid this, even though it improves damage drastically, because it will leave you more vulnerable.

After those three items have been purchased a Kindle Gem will give you a small boost to health and a 10% cool down reduction which will speed up your ability to stack Siphoning Strike.

Mercury's Treads will then give you a bit more speed and magic resistance, but most importantly the 35 tenacity will get you into position to attack with out the worry of crowd control effects or allow you to escape those close calls.

Finishing your Trinity Force can never be done fast enough. The huge bonus in damage provided by this item will allow you to farm Siphoning Strike without weakening minions prior to the strike(If you have been actively stacking it). The reason this item is so essential to all Nasus builds is Nasus has one primary source of damage... Siphoning Strike. This ability is an empowered auto attack, so by hitting the spell button you charge your Trinity Force(or Sheen) and when you strike Nasus does the damage from Siphoning Strike's base damage, Siphoning Strike's stacking damage, Nasus' Attack Damage, and an additional 1.5x his Attack damage from Trinity Force. Trinity Force effectively turns Nasus' Siphoning Strike into a short cool down nuke when stacked properly.

After that I finish of the Shurelya's Reverie(Kindle gem + Philosopher's Stone) to increase my health, health regeneration, mana regeneration, and cool down reduction even further. Shurelya's Reverie also has an additional active ability which speed up all friendly champions in the area by 40% for 3 seconds. With this ability being on a 1 minute cool down, it becomes a good way to chase opponents or escape while saving your Ghost for only the most drastic of occasions.

The last staple item to be built is Warmog's Armor. This will allow you to tank hits long enough to kill an squishy characters on the enemy team during a team fight and coupled with Whither will allow you to dive most enemies under their turrets with out worry.

From here you must decide what kinds of defense you need to build to survive as long as possible. I always lean towards Force of Nature as my next item since it has the highest health regeneration of any item in the game(even more than a fully stacked Warmog's Armor) and and the most magic resistance. This will effectively reduce damage taken from champions who deal magic damage, while Nasus' Whither should protect him from champions using auto attacks. Force of Nature also gives you another little boost of movement which is always helpful for tactical combat.

The last Item is the one that floats the most. Guardian Angel is an overall safe pick which will help if you are getting focused a lot, and allows your team to pick at the enemy while they are trying to down Nasus. I prefer a Bloodthirster in this last slot, though it is a difficult item for most people to use since you have to keep it stacked. Nasus should have an easy time stacking a Bloodthirster since he should be stacking Siphoning Strike anyways but be careful not to lose the stacks. One of the best reasons for using a Bloodthirster is, when coupled with Nasus' passive, he will have 45% life steal. This makes it so Nasus' Siphoning Strike is not only a massive amount of damage but also a 2.6 sec massive heal(at max cool down reduction). The Bloodthirster also boasts the second largest amount of damage of any item when fully stacked(fully stacked Sword of the Occult) and a large amount even when un-stacked. the 60 Attack Damage base will increase the amount of damage that a Siphoning Strike does by 150 when coupled with a Trinity Force, while to 100 fully stacked damage increases the damage of a Siphoning Strike by 250 when coupled with a Trinity Force. There are other options for items, like Thornmail, but these items tend to lack a balance and are often easy to counter. Still there are cases where they are necessary.

I will be adding more to this page, so please do not dock it for lack of content quite yet. I was hoping to get some early feed back on my lay out and have some Q&A so I know what else to include for others to better understand Nasus. I will also be adding some videos to show various aspects of Nasus' game play, with in depth descriptions of the events including what I could have done better in some scenarios. Thank you for any constructive comments and have fun summoners.