Rel said:
Wait a second here. I was under the impression that you COULD colaborate on making magic items BUT that the person who had the feat had to always pay the XP and that the item (Scroll in this case) would be of their "type" (i.e. Arcane, Divine, Bardish).
Am I wrong about this? Can you cite me a rule?
The creator of a magic item is the person who sets the caster level of an item as well as the person who pays the XP cost. They are also the person who sets whether certain items (like scrolls) are divine, arcane, or artificial. (

) Note that "bardish" is not a separate category from arcane.
Everything else about an item comes down to prerequisites. Specifically:
SRD said:
Note that all items have prerequisites in their descriptions. These prerequisites must be met for the item to be created. Most of the time, they take the form of spells that must be known by the item’s creator (although access through another magic item or spellcaster is allowed).
And:
SRD said:
Prerequisites: Certain requirements must be met in order for a character to create a magic item. These include feats, spells, and miscellaneous requirements such as level, alignment, and race or kind. The prerequisites for creation of an item are given immediately following the item’s caster level.
A spell prerequisite may be provided by a character who has prepared the spell (or who knows the spell, in the case of a sorcerer or bard), or through the use of a spell completion or spell trigger magic item or a spell-like ability that produces the desired spell effect. For each day that passes in the creation process, the creator must expend one spell completion item or one charge from a spell trigger item if either of those objects is used to supply a prerequisite.
It is possible for more than one character to cooperate in the creation of an item, with each participant providing one or more of the prerequisites. In some cases, cooperation may even be necessary.
If two or more characters cooperate to create an item, they must agree among themselves who will be considered the creator for the purpose of determinations where the creator’s level must be known. The character designated as the creator pays the XP required to make the item.
Typically, a list of prerequisites includes one feat and one or more spells (or some other requirement in addition to the feat).
The proper item creation feat is a prerequisite, just like any other aspect of the item. Thus, a vanilla magic sword requires the Craft Magic Arms and Armor feat, a caster level of 3x the Enhancement bonus, and a masterwork sword.
A Cleric 6 can provide the caster level requirement for a +2 sword, so long as he is working with someone who knows the CMAA feat. If he does provide the caster level, he is the item's creator.
SRD said:
The creator also needs a fairly quiet, comfortable, and well-lit place in which to work. Any place suitable for preparing spells is suitable for making items. Creating an item requires one day per 1,000 gp in the item’s base price, with a minimum of at least one day. Potions are an exception to this rule; they always take just one day to brew. The character must spend the gold and XP at the beginning of the construction process.
So, for any given scroll, the prerequisites are Scribe Scroll and the spell to be scribed. Generally, the same person who knows the spell is doing the scribing, so the issue never comes up.
In the event that duties are going to be shared, however, one character needs to be designated as the creator. The creator is responsible for paying the GP and XP costs to create the item, as well as for setting the caster level of the item.
For instance, take a scroll of Cure Light Wounds. It has two prerequisites: Scribe Scroll,
cure light wounds
We have a Wizard 3 helping a Cleric 2 to scribe it. Either the Wizard or the Cleric may be designated as the creator.
If it is the Wizard, the caster level may be set between 1 and 3 (the Wizard's max), and he will be charged (1 * CL) experience points. The scroll, when finished, will be an Arcane scroll of Cure Light Wounds - useless to the Wizard and the Cleric, but usable by any bard.
If it is the Cleric, the caster level may be set between 1 and 2 (the Cleric's max), and he will be charged (1 * CL) experience points. The scroll, when finished, will be a Divine scroll of Cure Light Wounds - useless to the Wizard, but usable by any Cleric.
Instead of the Wizard 3, we now have an Artificer 3 helping the Cleric. If the Cleric is the creator, the same rules as above apply.
If, instead, the Artificer is the creator, the caster level may be set between 1 and 3 (the Artificer's max CL when creating items - he only counts as CL 5 when meeting prerequisites*), and he is charged (1 * CL) experience points. The scroll, when finished, will be neither Arcane nor Divine, and so will only be useful to another character with UMD. Note, however, that since the Cleric is providing the Cure Light Wounds prerequisite, the Artificer need not make UMD checks to emulate the spell.
* - Note: This is one aspect of the rules I'm not entirely clear on, since I don't have the ECS with me at work. You'll want to look at the text before accepting the above as gospel ...
Also note, that when spreading the XP loss around the party, it's usually impossible to shift some of that loss onto the Fighters and Rogues, etc. They all have a caster level of 0, and most magic items cannot be created with a caster level of 0.
There are also some items - like the Cloak of Elvenkind (creator must be an elf) and Boots of Striding and Springing (creator must have 5 ranks in the Jump skill) - that force the creator to meet certain prerequisites, which cannot be met with the aid of another.