I started a Aatrox build when i was only level 25 (a long time ago lol) which was dumb because i didn't know ****, i'm ranked now and i'm re-doing this awful Aatrox build which had items like "Statikk Shiv" and "Black Clever" and like no defense items. So i'm making a new Aatrox build now that i'm ranked and i'm making it for season 4. So bare with me, and advice is welcome :)

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Top-lane
The sustain from Blood Thirst keeps Aatrox’s health topped off, allowing him to farm throughout the laning phase. Aatrox excels as a duelist, able to switch to Blood Price for heavy burst damage when trading with his lane opponent. After the exchange, Aatrox can toggle back to Blood Thirst to top off his health. When he’s ready to finish the job, Massacre adds significantly to an already potent burst combo.
If the lane isn’t going Aatrox’s way, the knock-up effect from Dark Flight can be used to set up ganks for his jungler. Or, if Aatrox has bullied his enemy out of lane, he can push aggressively, safe in the knowledge that the disengage from Dark Flight and Blades of Torment’s slow will aid his escape when enemies come charging. Even when things go totally wrong, Blood Well offers a second chance to secure kills or make a quick exit.

When Aatrox takes fatal damage he is healed for the amount currently in his resource bar. Landing a fatal blow on him while the resource bar is low will result in him reviving with a lower amount of health.
Unlike other reviving champions, Aatrox's Blood Well revive is rapid and grants him invulnerability during this time which allows him to quickly rejoin a team fight after being dropped to critical health.
When fighting him, consider his resource bar as part of his own health. (For example, killing him with a full Blood Well will make him return with a large portion of his hitpoints and if the fight was closely matched, he will most likely kill you.)
When Aatrox casts Dark Flight towards your location, avoid being knocked up by moving away from the center of impact.
Most players will aim the ability right above you or right behind you. So, moving closer to Aatrox at the time he casts Dark Flight will likely make the skill miss you.
In lane, zoning Aatrox out of combat will quickly drain out his Blood Well making him a much more vulnerable target.
While he can be built as a fighter, Aatrox's stats and kit are similar to those of a melee ADC, like Fiora or Master Yi. These champions are devastating as long as they are able to attack, but are extremely vulnerable to crowd control, and while Aatrox's Blood Well helps him survive, he is no exception to the rule, as a well landed stun or snare can severely hinder his combat abilities.
In particular, not only his damage but his in-lane sustain are dependent on him auto-attacking. Champions with strong blinds like Teemo or Quinn will give him fits during laning.
Inflicting Grievous Wounds can reduce his healing from Blood Thirst.
However, Grievous Wounds does not affect the health he regains from his Aatrox's Blood Well.
Without ability power (which likely won't be built), Massacre's intial damage is not a factor. The large attack speed and range bonus is a huge threat, but you don't have to worry about getting instantly burst-nuked by the activation.
The ability lasts long enough for most teamfights, but baiting Aatrox into using the ability to commit to killing you before a fight breaks out will remove the strong threat the ability presents in a teamfight.
However, it's recommended you only do this if you are a very hard to kill or catch champion, such as Lulu, Zac, Singed, or Karma.
Aatrox is auto attack reliant for not only his damage, but also his survivability. Reducing his attack speed by purchasing Randuin's Omen or Frozen Heart can help reduce both of those components greatly.

Team fights
Aatrox’s mobility gives him an innate ability to pressure enemy carries in team fights. Blood Thirst grants Aatrox plenty of sustain as he tangos with enemy initiators and tanks. When he sees an opportunity to reach an enemy carry, Dark Flight closes the gap and allows the punishment to begin. When Aatrox is in deep, the area of effect burst and extra range from Massacre, and slow on Blades of Torment prevent high-value targets from escaping. All the while the consistent healing from Blood Thirst and resurrection effect from Blood Well keep him alive long enough to cut through enemy squishies.
If Aatrox’s team is on the defensive, a well-aimed Blades of Torment can slow multiple enemies and open a window for retreating allies to slip away. Alternately, he can kite enemies with Dark Flight, and create an opportunity for the remainder of his team to turn and counter-initiate. If Aatrox is focused, Blood Thirst’s sustain and the Blood Well keep him in the fight, giving his teammates an opportunity to cut through foes as he resurrects and delivers the killing blow..