Create a magical item through Wish spell

[Jay R]

The core description of the Wish spell allows to use it for create a magical item up to the value of 25000 gp.

It would be a reasonable request to create an item of higher value, if the caster provides experience points and gold pieces to compensate the difference?

The 25,000 gp cap is for non-magical items only. This is a huge loophole. You can't wish for a galley, but you can wish for a galley that flies.

For this reason, many DMs apply the 25,000 gp cap to magical items as well. Let's assume such a DM, and then try to answer the question, because that's the only case in which it applies.

OK, we assume DMs who know that they are the final authority, just like the rulebook says. In that case, they'll have to make a judgment call,

And the crucial thing about judgment calls is that different people make them differently.

Your idea sounds fairly reasonable to me, but if I had to make the call, there are several issues I'd consider.

Do you have the ability to make that item yourself? The correct item creation feat, necessary spells or skills, and high enough level? If a Fighter wants to add her own XPs and gold coins, I'd probably say "No", simply because a Fighter can't do that. You get one effect. Perhaps with one wish you can ask to be able to add GPs and XPs, and with the next wish you ask to create the item.

Do you also plan to put in the extra time?

Who granted the wish, and what is their approach?

Etc. There is no simple answer that all DMs would agree on.

For example, here is my approach to wishes, as taken from my "Rules for DMs" document.

52. Wishes ought to be a social contract between the players and the DM. Don’t try to screw up the game, and I won’t try to screw up your character.

a. If a game system has clear, unambiguous limits for wishes, and a wish falls within the limits, then it should work as intended.
b. There is no sentient entity processing the wish. It is pure magical effect – akin to programming a computer. There is neither benevolence nor malevolence involved. The risk of a wish is the same as the risk of a car or a power saw; it goes where you steer it, not where you intended to steer it.
c. Unless it will screw up the game, the DM should follow the exact wording of the wish. This is usually, but not always, the same as the intent.

i. Following the exact wording of the wish does not mean abusing homonyms. If they ask for an extra feat, they don’t get extra feet.
ii. Following the exact meaning of the wish does not mean a bizarre, unlikely meaning. It means the most reasonable meaning of those exact words.
iii. If it took you more than a few seconds to come up with that interpretation, then it isn’t the obvious meaning of those words.

d. Wishes should rarely go wrong.

i. The best way for a wish to fail is to have no meaningful effect at all. Wasting a wish is well-attested in fantasy literature. It doesn’t hurt the game or the PC.
ii. When a wish actually goes bad, it should not cripple or destroy the PC, but at worst put the character in a difficult and threatening situation. Difficult and threatening situations are a DM’s stock in trade.

e. A wish will be fulfilled in the simplest manner possible. If a player wishes to have the only sword in the world, it is easier for the magic to put him and his sword on a separate world than to find and destroy every other sword on the primary gameworld.
f. An unselfish wish is always much safer. Wish for bumper crops near the village, or for the plague to end, and the magic flows much more smoothly.
g. A wish grants one effect. If the PC wishes for a sword and a shield, then he gets a sword. The shield is another wish. If he has two wishes, he gets the first two effects requested. If he wishes to travel to another continent to be introduced to the king and marry the princess, then he gets the travel and to meet the king, and his wishes are done.

i. Among other things, this means that long contract-like texts of legalese won’t work. Only the first clause is enacted.

h. The primary principle remains this: Don’t try to screw up the game, and I won’t try to screw up your character.

These rules were written for myself, for the way I run games. I am not saying that anybody else “should” run a game this way. These rules exist to help me be consistent, and so my players can know what to expect.

Anybody else is free to use them as guidelines, to modify them, to use some but not others, or to ignore them altogether, as seems best to you. Not everybody agrees on how to run a game, and there's nothing wrong with that.