Arsonist

Fire Starter.  The arsonist's weapon attacks deal an extra 9 (2d8) fire damage on a hit.  In addition, those attacks also light any flammable objects that aren't being worn or carried. 

Destructive.  The arsonist deals double damage to objects and structures when it deals fire damage. 

Alternate Ability Scores (Optional).  If you decide to include the Spellcasting feature, the arsonist's Charisma score equals 16, and it's Strength score equals 10.  You might need to change the weapon attack modifiers accordingly.         

Spellcasting (Optional).  The arsonist is a 3rd-level spellcaster.  It's spellcasting ability is Charisma (spell save DC 13, +5 to hit with spell attacks).  The arsonist has the following sorcerer spells prepared: 

Cantrips (at will):  create bonfire, fire bolt, light, prestidigitation

1st level (4 slots):  burning hands, chaos bolt, magic missile, shield

2nd level (2 slots):  blur, flaming sphere, scorching ray 

Elemental Adept (Fire).  The arsonist ignores resistance to fire damage, and when the arsonist rolls fire damage, it can treat any 1 rolled as a 2.  

Improved Fire Magic (Spellcasting Only).  When the arsonist casts a spell that deals fire damage, it can roll a d8 and add the result to one damage roll of the spell.

Molotov (2/day).  The arsonist throws a flaming bottle of rum at a designated area within 60 ft. of itself.  Each creature within a 20 ft. radius, 5 ft. tall cylinder must make a DC 13 Dexterity Saving Throw, taking (4d4) fire damage on a failed save, or half as much damage on a successful save.  The flames remain in the space for 1 minute before dissipating.  While in the flames, a creature takes (2d4) fire damage at the start of its turns.  The flames ignite any flammable objects that aren't being worn or carried.             

Torch. Melee Weapon Attack: +3 to hit, reach 5 ft., 1 target. Hit: 2 (1d4) bludgeoning damage.  The target must make a Constitution Saving Throw, taking 4 (1d8) fire damage on a failed save, or half as much damage on a successful one.              

Longbow with Flaming Arrows. Ranged Weapon Attack: +5 to hit, range 150/600 ft., 1 target. Hit: 8 (1d10 + 3) piercing damage. The target must make a Constitution Saving Throw.  The target takes 9 (2d8) fire damage on a failed save, or half as much damage on a successful save.              

Alchemist's Fire (4/day).  Ranged Weapon Attack:  +5 to hit, range 20/40 ft., one target.  Hit:  2 (1d4) fire damage.  The target takes 2 (1d4) fire damage at the start of its turns or until it uses an action to make a DC 10 Dexterity check to douse the flames.