Most people don't play Nasus as a spellcaster. in fact im certain barely anyone does, but I do. I thought I might share with the LoL community my Nasus spellcaster build. The reason I started to play Nasus as a spellcaster was that i found that there were better pushers than him and that a lot of his spells are quite good if spamable combined with AP. This whole build revolves around the use of cooldown reduction and the ability to spam your spells. THIS IS NOT MENT FOR JUNGLING OR SOLO LANE.

Nasus is actaully a pretty good spellcaster when played right. I can say I have had a lot of personal success with this build but it is up to you to try it out.

This build is so that you can creep farm super effectively and hit like a truck with your Q spell since the about of mana you have at your disposal and the fact of it having such a short cooldown.

Spam Q as much as you can for last hits
Spam E as much as you can so that you can damage coming minion waves, as well as remember that w/ the delay to lead your target
Build W last w/ only taking 1 point in it at the start for the utility
Your R spell is great for turret diving and pushing w/ a low cooldown it will start raking you in the kills
Take ignite for that last damage output incase they are running away and you cant catch up to them for some reason
Take flash just because it is really handy to have

Siphoning Strike - Nasus strikes his foe, dealing damage and increasing the power of his future Siphoning Strikes if he slays his target.
Nasus's next attack will deal 30/50/70/90/110 ( + ) physical damage. Siphoning Strike permanently gains 3 damage whenever it kills an enemy.
Cost
20/25/30/35/40 Mana
Range
300
Wither - Nasus ages his target, decelerating their movement and attack speeds over 5 seconds.
Nasus ages his target, slowing their movement and attack speed by 35% and reducing it further by 3/6/9/12/15% each second for 5 seconds.
Cost
100/100/100/100/100 Mana
Range
700
Spirit Fire - Nasus unleashes a delayed spirit flame at a location, dealing damage and reducing the armor of enemies who stand on it.
After a brief delay, the target area becomes desecrated for 5 seconds. Enemies in the area have their armor reduced by 20/25/30/35/40 and are dealt 20/34/48/62/76 (+0.2) magic damage each second.
Cost
70/85/100/115/130 Mana
Range
650
Fury of the Sands - Nasus unleashes a mighty sandstorm that batters nearby enemies. While the storm rages, he gains additional Health and drains nearby enemies' max health and converts it into bonus damage for the duration of the skill.
Nasus becomes empowered in the sandstorm for 15 seconds, gaining 300/450/600 health. While the storm rages, he deals 3/4/5 (+0.01)% of nearby enemies' health each second (240 damage max per second) as magic damage and converts it into bonus attack damage.
Cost
150/150/150 Mana
Range
20
Soul Eater - Nasus drains his foe's spiritual energy, giving him a natural 10/15/20% lifesteal. The lifesteal value increments at levels 1,6, and 11.

some items are replaceable in certain situations sometimes it may be better to get a catalyst the protector or banshees vail in stead of maybe the soul shard or a guardian angel in stead of a deathfire grasp. REMEMBER THIS IS A BUILD IT IS NOT FINITE USE WHAT IS GOOD IN YOUR SITUATION AND WHAT YOU FEEL COMFORTABLE PLAYING W/. each of these items is to help your survivability as well as increase mana regen and cooldown reduction.

Pros:
- spamable spells
- build w/ items for survivability
- still an effective pusher
- very short cooldowns

Cons:
- very late game oriented
- slightly squishier than normal