When it comes to creating a backup character, does your table follow a forum of discussing this character's design with all the players?  Or is it is assumed that the backup character will be of the same class; or at minimum the same function and role that that your primary character has (ie. a Martial who can Tank; or Spellcaster who is the party's diplomat, etc).  Or is there no expectations or additional considerations required, and your backup is whatever you feel like having.  A complete 180 turn if you want.  Or maybe, you have the freedom to scrap your first backup design after Session 1 or 2 and make a new character anticipating the party's weakness that may result in your primary character's demise? 

Is there an etiquette or protocol that should be followed? 

I understand that players can put too much emphasis on character design and sometimes should just focus on playing the game; but there should be a consideration for the other players at the table.  For example, if a player's Fighter dies and that player introduces a Ranger or Paladin; and with them comes proficiency in new skills and a high WIS (for Ranger) that allows them to be the party's scout, or high CHA (for Paladin) to serve as the face of the party, then I can see how a player with an existing character may feel like this is taking their role way; or worse, be perceived as a commentary that they are not at playing their function well.  But then again, I can also see how this doesn't matter, and that 5e provides many options for the DM to ensure all players can have an impact on the game sessions.  I have heard that 5e isn't built to require different classes in order to run a campaign; so if the party ends up with 4 Wizards and a Bard then what's the problem? 

Thank you in advance for the comments.  

I think that games are there to be fun, and a negotiation with fellow players is good, but changing types of character is fine.    A paladin doesnt have to take over as the face, and scouts can work in pairs.   

I only require communication about characters during creation in order to avoid the steppings on toes. I don't want a party of five Champion Fighters turning up.

So far, I've only ever had one character die at any given time, so post-session zero, I don't generally require that players talk to each other about their new characters. They just let me see the sheet, I OK it then they bring them along to their next session. They already know the party composition, so they can fit their new character in. If there were multiple deaths, then those who'd died would have to communicate and negotiate. Otherwise, it's only if their character niche is too close to someone else's that I'd tell them to ask - it might be ok, it might not. I've never had that come up yet though.

We talk about what we want to play as we're starting, but at the same time if someone dies?  I want them to play something they want to play, and not what the table wants to play.  They already lost their character, they shouldn't also lose the agency they have as a player and be forced into something that they aren't going to have fun with.  A good DM will swing the balance of the fights to the table dynamic so that it is challenging based on the party composition rather than just being challenging for the sake of being challenging. 

If somebody dies, they can choose to come back as anything they want.

It's polite, when creating characters, to try and avoid stomping on other player's shticks. This is not specific to backup characters, however.

Our group only recently started talking about backup characters because we almost had a TPK.
It's not really a topic with our group and is not something that is standard for us, so we have no set way of creating one.

Quote from Pantagruel666 >>

It's polite, when creating characters, to try and avoid stomping on other player's shticks. This is not specific to backup characters, however.

 So true. If I had a character die I would make a backup that wouldn’t step on others toes. Same as when deciding what to play to begin with. Hopefully the player is as polite to take that into consideration. 

One of the suckiest games I ever played in had five of the players try to build characters with the same niche in mind. It got boring and old very quickly - despite the DM actually having some good skills. It was made worse by the fact that every player refused to talk about what their characters would be. I declared what I was going for, then everyone else.remained silent. Then five of the six other players turned up on the day with similar builds, so I ended up effectively with no subclass. So annoying.

That's why I always strongly advise players to find unique niches and roles in the party. There can be overlap...but they each need to find a niche in the party to occupy.

That's the main etiquette I want at the table. I insist on it when I'm DM. If your build is encroaching in someone else, then speak to them and hash things out. It's possible to have two tanks for example, but you need to know how to differentiate characters and whether there's space in the party for that. Trust me, you don't really want five tanks.

The one thing I'd do is talk to my DM and ask what they feel is most appropriate for the setting and group. That way you know you are on good footing as you share what you are doing with the rest of the players. It may spark them to do the same.