To use this build, you should already know how to play Renata Glasc.
This is not a guide on how to play Renata Glasc. It's a guide on how to use Renata Glasc as an AP Carry.

Only follow this guide if already you know how to play Renata Glasc.

I know what you're thinking already:
"Someone is delusional and made this guide to troll people."
You are probably right. But also, no.

The primary purpose of this build is to maximize the %Max HP damage from your Passive, Leverage.
Using this, you are able to quickly dispose of enemy tanks with the help of your team, using your own abilities to facilitate their gameplay which makes you an excellent teamfighter.
To elaborate on why you build full AP and not any other item build, let's look at the numbers here.
Renata Glasc's Passive has an AP Ratio of 1% − 2% (based on level) (+ 2% per 100 AP) of the target's maximum health. For somebody who plays Varus, these numbers may immediately ring a bell.

Like Renata herself, this build requires you and your team to be on the same page, as a lack of coordination means that you can not get your damage off, which means your team will be playing 4v5. However, if you and your team are in sync and play off each other, this may as well be the strongest lategame teamfighting pick in the entire game.

This build is best played in the Bot Lane as a carry because you simply have access to more gold. You will be able to reach power spikes faster and enable your team to do huge damage that way.
As a support, you will simply be weaker at every point of the game, meaning you may as well build traditional support items.
Furthermore, your playsyle is going to be the same as any other marksman, because your passive, which applies on auto-attacks, is your main damage.
Your other abilities are important, but you functionally become an ad carry, so playing in the marskman role is just the best fit here.

Your Passive AP Ratios are comparable to AP Varus, which becomes apparent when you hit full build. In teamfights, you can melt tanks as if they weren't even there, which makes you an excellent front-to-back teamfighter.
In addition to bringing a lot of damage to teamfights, you also have the utility of a support, being able to shield your teammates and give them a second chance through your W. Your Q should be immediately recasted unless absolutely necessary, because hitting the Q will lock you out of auto-attacking, which is not something you should be aiming for as APC.

Lastly, as Renata Bot, you have a lot of synergies with other supports that traditional Marksmen and even Mages don't have.
You are able to stack your shields on top of enchanters, empower certain ally abilities, out-sustain your opponents, follow up on ally hooks with your own, the list goes on.
Your ultimate is slow, but if you couple it with another ultimate like Seraphines or Namis, your R becomes utterly unavoidable.

This build has some glaring issues. Depending on who you ask, they may outweigh the benefits, but this is up to personal opinion.

Firstly, your early waveclear is terrible. You rely on your support to constantly push the wave for you because you just don't deal enough damage to minions early on, and your attack speed pre Recurve Bow is simply worse than your peers.

You also have a very hard time farming. Due to Renata's base AD being overnerfed, you are not able to get CS under tower under normal circumstance. DO NOT LET THE WAVE CRASH INTO YOUR TOWER unless your life is in danger.

Another downside is that you are chained to at least one teammate. This pick is not supposed to fight by yourself as you can not proc your passive on your own. As a consequence, 1v1 fights are impossible.

Lastly, you are both immobile and squishy. You can fix the latter by building defensive items, but until you finish your core build, you will have these weaknesses and just need to live with them.

Over the course of the game, you'll encouner a few peculiarities of this playstyle.

• You can quickly kill backline minions if you have both Nashor's Tooth and your Starting Item.Do not sell That Starting Item until your second item.
• Despite the weird picks and the weird items, your playstyle is the same as that of a traditional marksman. Your support may get funny ideas of what kind of things you need, but they are wrong. They just simply need to play as if they played with a normal, albeit weaker, adc, and it'll work out just fine.
• Unless you are way behind in farm, you will want to stick to your team like a piece of gum. You are practically useless in 1v1s, so only split off from your team if there is easy gold to be farmed, then immediately join them again.
• If you have any allies with built in Damage Over Time, these will be your highest priority. DoT instantly procs your passive. Additionally, Ivern, Leona, Lulu, Milio, Nami, Sona and Yuumi can instantly proc your passive, as some of their abilities apply from your Auto-Attacks.
  IMPORTANT NOTE: As of patch 13.17 This only applies to Abilities, not items or runes. Apparently Liandry's Yuumi was just too strong, I guess. **** you, Riot.
  Update: As of patch 14.3, Liandry's Anguish specifically can proc Renata's passive again. This may be an oversight by the devs, but this opens up the possibility for more bot lane synergies. Let's hope it stays that way.

If Renata gets nerfed, I'm driving all the way to Riot HQ and throw kitchen knives in the office. :D That being said,

Good Luck and Have Fun