Well this is how I am going to run evocation magic, using Fate Core. Each spellcaster has 3 skills
Lore: supernatural awareness and arcane knowledge
Will: conviction and belief - represents the power of your spells
Focus: mental discipline and ability to control magical energy
Gathering Power
To achieve any effect with magic you need to first gather magical power. Fortunately magical energy is the essence of life and emotions; you need only a moment to focus your will or channel an emotion to power a spell. However if you want to put more effort and power into a spell its possible to take a create an advantage action; use Will when getting emotional, Focus for intense concentration, and Lore to draw magic from your surroundings. The difficulty is equal to the ambient level of magical energy; typically this is Fair (+2), but in the Nevernever this could be Moderate (+0) at worst, while a magical dead zone would likely be at least Superb (+5). In a magically sealed environment, such as within an uninvited threshold or circle of magic, use the thresholds strength or the Will of the Spellcaster. If this action is successful, you may use any free invokes gained to cast your spell.
Casting the Spell
Now the energy is gathered, you need to focus and release it safely in the form of a spell. Choose one of the following actions. Unless you are casting a rote spell, you must also take a point of mental stress.
Overcome: Use Will to deliberately hex a machine or piece of technology, or overcome an obstacle or problem using magic, such as picking a lock or lighting a fuse. Use Will to remove an aspect created with magic (known as a counterspell); the spell’s caster may defend with Will.
Create an Advantage: Use Will to alter the environment with magic, or place a mental or physical aspect on a target. This may be an impediment, such as Trapped in Ice or Dazzled, or defensive in nature, such as Veil of Invisibility or Entropic Shield. Characters can defend against this with Athletics or Will as appropriate.
Attack: Use Will to harm someone with magic, whether conjuring fireballs or removing air from their lungs. Targets can defend against this with Athletics or Will depend¬ing on the nature of the attack.
Defend: Use Will to defend against hostile magics or other supernatural effects (known as a counterspell). If you have a defensive aspect on yourself you may use Will to defend against an appropriate action; a force shield against physical attacks or a veil against Notice rolls etc.
Backlash and Fallout
If your skill result is greater than your Focus skill, you have failed to properly harness the magical energies in the spell; your spell may be successful, but you must deal with the chaotic effects of uncontrolled magic. Each shift of uncontrolled power (the difference between you skill result and your Focus) must take the form of either backlash or fallout. Backlash is when your body absorbs this chaotic energy; you must take a point of either mental or physical stress for each shift assigned. Fallout represents uncontrolled magical energies leaking into the environment. In game terms, the Gm gets to place an aspect on the scene using the shifts you assign as a passive opposition to any attempts to overcome it.
Harry Dresden is trying to cast a fireball at a ghoul in his office. He makes a Will roll getting a result of 7; since his Focus is just +4, Harry decides to take all of those shifts as fallout. The Gm places Office on Fire on the scene, whether the spell hits the ghoul or not. Anyone trying to remove or get past the fire requires a Good (+3) result or better.
Rote Spells
You start with a number of rote spells equal to your Lore, plus any gained from the Refinement power. Words insulate a spell caster from harm when casting an evocation spell and each rote spell must be named and spoken when cast; typically this is in another language to prevent you from accidentally casting it. Each rote spell has a defined element and type of action – you cannot modify the basic nature of a rote spell, but you may gather power to increase the power of the final effect.
Specializations: Each specialization provides a +1 bonus to Focus, Lore or Will when using a specific element or type of thaumaturgy.
Crafting Specializations: Each specialization provides a +1 bonus to the Capacity, Frequency or Potency of any items you create. Any Focus items you create have a Capacity equal to your Lore. Any Enchanted items you create have a Frequency of 1, and a Potency equal to your Lore.
Focus items: Each Focus item slot provides a +1 bonus to your Focus, Lore or Will relating to one element or type of thaumaturgy, used either offensively or defensively. A blasting rod could provide a +1 Focus when using fire offensively, or a shield bracelet may add +1 to Will when using defensive spirit magic. If you want to be able to apply an additional element or type to a focus, all elements must share the same bonuses; for a staff that provides a +1 Focus to offensive fire magic, and +1 Will to defensive fire magic, adding the element of water would cost an additional 2 focus item slots. No single item may have a total number of bonuses that exceeds its Capacity.
Enchanted items: Each enchanted item slot represents an item containing a spell, usable a number of times each session equal to the item’s Frequency. Activating the spell is just like casting an evocation spell using the item’s Potency; it is not subject to fallout or backlash but you cannot gather power to increase this value. You may increase an item’s Frequency by reducing its Potency by the same amount. However, you cannot reduce an item’s Potency to less than 1 plus your Potency bonuses. You may also reduce an item’s Potency by 1 so that it can be used by anyone; such as a wand that requires a word to activate or a scroll containing a spell.
Each additional enchantment slot can be used to either increase an item’s Potency by 1, or its Frequency by 2. However, no item can have a Potency rating of more than twice your Lore without a very good rationale and a ton of baggage.
Enchanted items may need a skill to use effectively, such as staff of fireballs that requires a Shoot roll. In this case use the skill or the item’s Potency, whichever is lowest. If an item has been drained of uses, you may still use them but you must take a point of mental stress when doing so.
Armour: Armour is a special type of enchanted item that provides an Armour rating equal to the item’s Potency/2, rounding down. Each time armour is activated it lasts for an entire scene or until it removed by magic; you may defend against such actions with Will.
Potions: Potions are a special type of enchanted item. They can be used by anyone without needing to reduce their Potency, but can only be used once. If you have any enchantment slots free at the start of a session, you may declare any of these as potions. Alternatively, you may create an advantage using lore, to have one on hand (or a second if you succeed with style). Unlike regular enchanted items, you may gather power to bolster the effectiveness of the potion, creating an advantage such as Empowered Potion.