Conflagration

You start a wildfire on any 5ft square you can see that catches onto anything it touches. The flames take on whatever colour you wish. You have no control over it once it is set and it burns uncontrollably for the duration and nothing can put it out, apart from a Dispel Magic. The growth rate of the fire is up to ten 5ft squares per turn, in any direction, so long as it all connects to the original targeted area. At the end of the spell, the flames extinguish, leaving behind whatever scorched earth is left and a clear level of destruction. Its direction is affected by any winds in the area or spells such as gust, but these just seem to cause the fire to grow in the direction it is being blown.

Any objects or creatures caught in the wildfire take 5d12 fire damage per round they are engulfed and are then set on fire, on a failed Dexterity saving throw, or half as much damage on  successful on, and are not set on fire. It requires an action to put the flames out on yourself and you must be outside the affected area. If you remain on fire, you take 1d12 fie damage at the top of each of you turns.

 Casting this spell at 5th level or higher increases the damage by 1d12 per level abve 4th.