Morrowind:Spellmakers

Spellmakers are NPCs who can make custom magic spells for you from your known spell effects. The ability to make custom spells is important to any player using a magically inclined character. Up to eight effects can be combined into a single, potent spell; spells can be tweaked to provide maximum effect for minimal cost.

Making Custom Spells
Custom spells can be made by talking to a merchant with the Spellmaking dialogue option. Each Mages Guild Hall has one such NPC from whom you can buy custom spells, with the exception of Caldera.

On the left side of the Spellmaking window you are presented with a list of all spell effects you have collected so far, which can be used to create the custom spell. Select an effect you wish to add, and a new screen pops up where you can set the range (self, touch, or target), minimum and maximum magnitudes, duration, and area of effect. These parameters determine the magicka cost of the spell, the chance of successfully casting the spell, and the gold cost of making it. Once you have finished setting the effect's parameters, you may then add additional effects (up to eight) if you wish. Finally, name the spell and then purchase it. For vampires spellmaking is only available in Mournhold.

The fee for scribing the spell is 7 times its Magicka point cost. Disposition and mercantile skill have no effect.

Spell Cost
The cost of a spell is the sum of the costs of all its effects. They can be calculated as follows:

600px

See Spell Effects for the base cost.

Note that every variable (max, min, duration and area) is treated as at least 1.
So while it is possible to create a spell with 0 pts of fire damage for 1 second without area of effect, it will still have its spell cost as if it had 1-1 pts of fire damage for 1 second in 1 ft.

Also take note that as opposed to enchantments spells spread over a duration are more cost effective.
(Spell cost compared to enchanment cost charges you for one additional second, which has more of an impact when the magnitude is high. So a spell with 100 pts of fire damage for 1 sec costs 50 mana while a spell with 50 pts of fire damage for 2 sec costs only 37).

A maximum of eight effects can be added to a spell, but you can not add the same effect twice (except with effects affecting skills and attributes).

Casting Success Rate
The chance to cast a spell is calculated with this formula:

 

The preview value given by the spellmaker assumes that the caster's Fatigue is at half. In correspondence with the formula, with a full fatigue bar the success rate is about 25 percent higher than what is shown; e.g., a chance of 81 is actually 100 when fully rested.

Multiple-effect spells will belong to the school of the effect that you have the lowest chance of successfully casting. For example, if you create a spell with Paralyze (Illusion school) and Damage Health (Destruction school) effects, and your chance of casting the Paralyze portion of the spell is lower than your chance of casting the Damage Health portion of the spell, the created spell will be tagged as an Illusion spell. If your Illusion skill increases to the extent that your chance of casting the Paralyze portion of the spell becomes higher than your chance of casting the Damage Health portion, the spell will be re-tagged as a Destruction spell.

Spell-makers
These NPCs will allow any character to create what spell they desire, but at a price.