Hey, all. So I'll soon be playing in a Dragon Heist campaign with a few friends, and I'm looking for advice on what the best build is for this module. 

For info, it'll be pretty casual game, on the larger side (6-7 people). The DM's very easygoing, and he'll probably allow anything as long as it's not an obvious mechanics abuse.

I'm about as unfamiliar as one could be with the module, but from what I've heard, it's very intrigue and RP heavy. With that it mind, I'd expect that charisma-based classes and rogues will particularly shine.

Essentially, I'm looking for a build that can contribute to the party as well as allow for some great RP potential. And since Dragon Heist seems a lot different from most other modules, I thought I'd ask the experts. 

Any thoughts?

Paladin, Fighter or Barbarian.

You have to have some muscle or the party will have a hard time.

To be honest, what others play matters more than anything, especially if you have a good DM that will help you shine even if your party make up doesn't align perfectly with the expectations of the adventure. Find out what classes/subclasses are going to be present, and with 6-7 people present, there's room for serious issues on this front (been there, done that, got the t-shirt). Unless you get first dibs and the others respect that.

I don't know much about the campaign, but given off on what you've said, something like a Bard, Rogue, or Paladin. I've also heard a Rogue with a few levels into Wizard is effective and fun, but I've also heard it the other way around.

In the end, play what you want. Don't feel like you have to optimize for the campaign. Like what Linklite said, there are a lot of people playing so there is no need to worry about what would be best.

This was an easy adventure, as I remember it. Your success will hinge far less upon your characters' abilities and far more on your ability to connect dots and pursue leads.

The only character building advice I have is: Make a character who's willing to talk to strangers.