[D&D 3.5]How do wizards research/craft a new spell?

[AugustusGloop]

I'm playing in a campaign that is mostly downtime, a lot of master/apprentice rping, and my conjurer would like to start working on new spells. I've done a little looking, but there doesn't seem to be much of a system in place for costs/time etc. Has anyone home brewed something, or can anyone point me at a system with some crunch for my wizard with ideas running over?

[Daefos]

Page 198 of the Dungeon Master's Guide has some spell creation guidelines. There's a bit more to it, but it would basically cost 1,000gp a week and require a number of weeks equal to the spell's level.

[Fizban]

I don't remember where it is, but somewhere in core the standard rule is one week and 1,000gp per level of the spell. Then you make a spellcraft check, and if you succeed, and the DM is okay with the spell, you can learn it (but it still takes up a spell known slot if you have a limited spells known list, otherwise it just goes in your book). Spell research requires access to an arcane library, which is usually handwaved if you can find a friendly wizard's guild. If you want to buy one yourself, it's at least 10,000gp to find all the books in a big city, and you'll need something big to carry them in.

Ack, ninja'd with a page number.