5e Races for S&W: Dragonborn

Dragonborn

Dragonborn are humanoids bearing draconic traits. At the Referee's discretion, they might be from communities of dragon-worshipers, adventures who made pacts with dragons for power, or have other origins. They have lizard-like heads, scaled skin and talon-like hands. They are most often fighters, due to their great bulk and physical power. When a dragonborn rides into town at the head of a mercenary company, locals are apt to stand in awe and unease. 

Dragonborn may bear the scales of red, white, blue, green or black dragons, and have immunity to the according element: fire, ice, lightning, poison, or acid. In addition, the larcenous hoarding instinct of a dragon runs through them, and dragonborn can focus to sense the presence of precious metals and jewels within 10', although they can't tell the amount or type, and this sense is blocked by more than 2' of stone or a sheet of lead.

Dragonborn may advance to 4th level as Thieves or Clerics, to 6th level as Magic-Users (up to 7th or 8th level with an INT of 17 or 18 respectively) or indefinitely as a fighter. 

Summary

Immunity to 1 element, senses precious metals and jewels in 10', blocked by 2' stone. sheet of lead

Limited to Thief or Cleric 4, MU 6-8, may level as Fighter without limit.

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I'm not really a fan of the idea of dragonborn communities or populations. It feels to me like reskinned Klingons. I'm much more interested in the idea of individuals trading their humanity and service for immediate power. That way, each dragonborn is an individual with their unique story, not just another member of a preexisting race. If you wanted more of a balance between these approaches, I'd look at communities of human dragon worshippers, like in Arnold K's Drakencults, and the dragonborn is a champion raised up by that dragon to serve their will. 

This connection to a dragon in the backstory is largely up to the player to describe. Common tie-ins might be that the dragonborn is treasure-hunting to send great works or artifacts back to the home hoard, or hunting down a rival dragon who offended their master in the past. If the character is a rogue dragonborn, taking their powers but running from their old master's influence, that has a great deal of material for roleplaying, and hooks for the Referee to use. 

Since dragonborn are a relatively known race, and they don't have the tiefling's contentious history, there's not much for me to write about them. I must say I like the feel of dragonborn more than lizardmen. I never got the appeal of those. As far as 'monster' races go, this one ranks pretty highly for me, up with minotaurs. The exact place in lore and popular opinion of dragonborn is really up to individual Referees and the tone they intend for their game. 

Another neat take on dragonborn is this one by Marquisat: Dragonborn are Irradiated Humans.