Welcome. The main idea of this build is to set Nasus with tanking ability, while still giving him some attack punch. Also, beside Siphoning Strike (SS), my second Ability focus on Wither.

Your principal ability is Siphoning strike, I won't talk much about it, because it have been explain often into other build. Use it to strike the last hit on Minions to improve your attack damage.

Wither reduce movement and attack speed of your target, so cast it on the Damage Per Second (DPS) character if you enter in a big melee fight, so that his attack rate will be greatly reduced. Never cast Wither and Exhaust on the same Hero at the same time. Exhaust will be perfect to reduced attack ability of a second enemy or to slow down again your target once Wither effect is over. Wither is also excellent to cut the escape of one enemy so that your team can swarm him to death.

The other big advantage of this build is the -40% Cooldowns it provide. That mean, Fury of the Sand and Wither will be available for casting more often. Early in game you will get a -30% Cooldowns (Your Glyph + Frozen Heart).

Note: originaly, with the Randuin's Omen at 15% Cooldowns, the current build was exceeding the -40% Cooldowns cap. In all cases, you can replaced the Cooldowns Glyph with Magic Resistance. Since the -40% Cooldowns was reached in late game (With the Randuin's Omen), you could still favor the Cooldowns Glyph to get a -30% Cooldowns during most part of the game, especially if you play in 3 vs 3 often, which leave you less time to get gold. However, with the new patch, the current built doesn't exceed the -40% cap. I also made slight modifications on the Mastery skills to keep the Cooldowns stats on the build at 40% .

In most case, follow the items build order proposed. However, an alternate build order would be the following. From the Randuin's Omen, you can decided to buy Banshee's Veil first, instead of the Randuin's Omen. This could be well indicated if the opposite team have many casters.

With the normal build, the Frozen Heart passive effect + Randuin's Omen active effect will greatly reduced the attack speed of every enemies around you. Add to this Wither and Exhaust and you have a DPS nightmare in hands.

However, the advantage of the alternate items build order is not only the boost of HP and Mana, but reside with the spell effect negated every 30 sec, which mostly will canceled the first main debuff cast on you while you or your enemy decide to strike. This is a nice defensive ability you might prefer to have earlier, if you prefer to balance the array of faculties at your disposal. The Banshee's Veil will also increase your Magic Resistence, which goes fine with the idea to balance your Nasus against many types of attack damages. After all, as a tank, you will have to eat all kind of hits.

Have fun = ) I hope you will enjoy this build.

Your constructive comments, recommandations and critics are welcome. I take also praises and flatteries = )