Base Class: Cleric
You draw your power from a dragon of immense power, acting as its herald and voice in the world. The dragon could be a deity such as Bahamut, Tiamat, and Sardior or potentially one of the progenitor dragons of Eberron. The dragon you draw your power from could also be an ancient dragon or greatwyrm to whom you devote yourself. These dragons cover a wide variety of alignments and goals, which means that clerics of this order could vary just as drastically in how they act and their goals. For example, a cleric devoted to Tiamat could be tyrannical leader building a following and hoard to bring Tiamat back into the material plane after the recent attempt by the Cult of the Dragon and Severin failed. A cleric of Bahamut could be wandering the land looking to heal the injured and sick or to follow in the Platinum Dragon's footsteps and help new and unlikely heroes against the forces of evil. A cleric of an ancient dragon might be sent out to extend the influence of an Ancient Chromatic Dragon who desires political influence and to collect more wealth for their hoard, while following the influence of an ancient metallic dragon might lead a cleric to set out to find interesting people, stories, and art to either bring back to the dragon or just tell the dragon about.
Sometimes these clerics are called heralds, "wyrmspeakers", or occasionally the "Breath of " their dragon.
When you select your dragon deity take note of their breath weapon damage type as it will be used for abilities in this class.
Bonus Proficiency
When you choose this domain at 1st level, You gain proficiency with Martial Weapons, you know the Draconic Language, and have proficiency in Arcana checks.
Disciple of Dragons
Also starting at 1st level, you can alter your spells to echo the power of your draconic deity. Whenever you use a spell of 1st level or higher that causes damage you can alter the damage type to match that of your deity. This damage type should be the same type as your deity's breath weapon, if your deity has more than one breath weapon damage type you can choose this damage for the day when you are preparing your spells.
Channel Divinity: Draconic Power
Starting at 2nd level, you can use your Channel Divinity to unleash your deities power upon your foes.
When you strike an enemy with a spell that requires a spell attack roll to hit a single target you can use your Channel Divinity to cause half of that damage to spread to enemies within 5 ft. Alternatively when you cast a spell that causes multiple enemies to make saving throws to prevent damage you can select a number of enemies in the area of the spell up to your Wisdom modifier and give them disadvantage on their saving throw.
Scaled Protection
Beginning at 6th level, you gain resistance to the damage type associated with your draconic deity.
Additionally as a reaction you can give an ally you can see within 30 ft. advantage on a saving throw. You can use this second feature a number of times equal to your Wisdom modifier (minimum of once). You regain all expended uses when you finish a long rest.
Potent Spellcasting
Starting at 8th level, you can add your Wisdom modifier to the damage that you deal with any cleric cantrip.
Chosen of the Dragon Deity
Starting at 17th level, you can use your action to activate an aura of draconic power that emanates in a 60 ft. radius centered on you. Creatures in this area have their resistance against your draconic damage type lowered. If they are immune to the damage type they become only resistant to the damage type, if they have resistance against the damage type they lose that resistance, and if they don't have any resistance or immunity to your draconic damage type they become vulnerable to that damage type. In addition, enemies in this aura have disadvantage on saving throws against your spells and you have advantage on attack rolls against them. Once you activate this ability it lasts for one minute and then it can't be used again until you complete a long rest.