User-Provided Mana Items

UPM items are pretty straightforward. You activate one by giving it spell power (spell slot or magic points) and meeting any other requirements it has (such as uttering a command word or paying experience points) and the effect happens.

Because the power is drawn entirely from the user, the degree of effect is based on the caster level of the user. A scroll of spell.fireball has range and damage as if cast by the user, rather than by the creator of the scroll.

The simplest model I've found for UPM items that I think will work is to remove the caster level component from the market price of the item. A UPM scroll will cost 25gp per level of the spell on the scroll, a UPM potion will cost 50gp per level of the spell of the potion, and so on.

This looks frighteningly low, in some ways. It costs only 300gp for a UPM use-activated single-use item (such as a potion or consumable wondrous item) of a sixth-level spell.

However, this still requires the user to use a sixth-level spell slot — one that he could otherwise have used to cast a spell that he knows or has prepared. This 300gp is not for the sixth-level effect, but for the ability to use a 6th-level spell slot on a spell the caster does not have prepared or does not know (and in this case, in fact, he need not even be capable of learning the spell).

The only place I'm concerned is with permanent, at will items. A UPM rod that gives the ability to cast a spell at will (that you don't know!) would cost 2,000gp per spell level. This doesn't bother me much with most classes, but it gives a potentially huge benefit to sorcerers, for the cost.

To create a UPM item, you must have the Create User-Provided Mana Item feat. It allows you to create magic items that draw on their users rather than on you, when you create the item.