How to Rogue

[ExiledOne]

Play that class until level 10 - at that point, your guild leader of the class you chose will allow you to go investigate other classes.
Complete this quest.

Do you need the sidequest? It is not listed as a requirement. Although it does point you to the Rouge's guild location.

[AskaRay]

Do you need the sidequest? It is not listed as a requirement. Although it does point you to the Rouge's guild location.

You may not need the sidequest... I know when rogue first came out, I did it first.
Though I was looking at the requirements and it wasn't listed, so you may not need to do it first.

[Niwashi]

You may not need the sidequest... I know when rogue first came out, I did it first.

I think that "Edelweiss, Edelweiss" sidequest got added because they needed a way to tell people in-game where the rogue's guild is located. The class unlocking quests show a quest symbol over the issuing NPC's head when you're next to them, the same as other quests do, but unlike regular sidequests, they don't show as quest icons on the map. We're expected to just head to the guild and seek them out when we want to unlock another class. However, as a guild that lore-wise is hidden and secret, and gameplay-wise was added after the game had been out a while, that alone would be a little problematic. Most existing players wouldn't be re-exploring out of the way corners of the main cities after each update.

So the most common pattern is that people would take that "Edelweiss, Edelweiss" sidequest that shows up on the map (and in any case is at one of Limsa's major hubs of activity) and that would take them down to where the Rogue's guild is located. At that point they find the NPC with the quest icon over his head who can offer the "So You Want to Be a Rogue" quest. But if you either know where he is already, or just come across him while exploring Limsa's Lower Decks, you can go ahead and just take the unlock quest "So You Want to Be a Rogue" first. You don't actually need to have done the sidequest that would lead you there. (The sidequest does offer a bit of background about how they're hiding, though, so it fits in as part of the Rogue storyline.)