Optional Rule: Spell Research
Some Wizards want the option of researching new spells in their downtime to fill out their spellbook. As an option, you might allow a character who uses a spellbook to perform this research at a cost.
Spell Access
Getting access to an existing spell requires time and money to find a scroll or spellbook that someone will allow you to copy from. Even then, there is no guarantee another wizard will have or be willing to part with the spell you are seeking.
Resources. Finding access to a spell requires at least one workday of effort and 100 gp in expenses. Spending more time and money increases your chance of finding the spell.
Resolution. A character seeking to find access to a spell makes a Charisma (Persuasion) check to determine whether they are able to get access to the spell. The character gains a +1 bonus for every workday beyond the first spent seeking someone willing to share, and a +1 bonus for every additional 100 gp spent on the search, up to a maximum bonus of +10. The monetary cost includes a wealthy lifestyle, for wizards have little respect for those who live in squalor.
The DC for finding the spell is equal to 10 + the level of the spell you are seeking access to. On a success, you gain access to the spell, and may use the rules for Copying a Spell into the Book found in the "Your Spellbook" sidebar of the Player's Handbook on page 114. On a failure, you may attempt the search again, but must begin anew in terms of both the time and monetary resources spent on the search.
Independent Spell Research
Alternatively, a character may attempt to perform independent research to recreate a spell that they have seen used, but which they do not have access to add to their spellbook. Independent research is time consuming, but is often less expensive and easier for wizards who lack social graces to pull off.
Resources. Independent research requires at least 50 gp in expenses for each level of the spell to be researched (thus, a third level spell requires 150 gp to research independently). Additionally, researching a spell in this manner requires at least one workweek. Spending more time and money increases your chance of successfully researching the spell.
Resolution. A character seeking to research an existing spell makes an Intelligence (Arcana) check to determine whether they are able to successfully research the spell. The character gains a +1 bonus for every workweek beyond the first spent researching the spell, and a +1 bonus for every additional 50 gp spent on the research, up to a maximum bonus of +10. The monetary cost includes a modest lifestyle, so that you can perform your research in peace and privacy.
The DC for researching a spell is equal to 10 + the level of the spell you are seeking to research. On a success, you have learned the secrets of the spell, and may use the rules for Copying a Spell into the Book found in the "Your Spellbook" sidebar of the Player's Handbook on page 114. On a failure, you may attempt the research again, but must begin anew in terms of both the time and monetary resources spent on the research.
Researching New Spells
Finally, a character may wish to create an entirely new spell which has never been seen before. This research is similar to Independent Research, but is far more difficult, time consuming, and costly. However, completion of this research can be incredibly rewarding, and can result in a good deal of social credit with other wizards.
Resources. Researching a new spell requires at least 150 gp in expenses for each level of the spell to be researched (thus, a third level spell requires 450 gp to research independently). Additionally, researching a spell in this manner requires at least one workweek per spell level. Spending more time and money increases your chance of successfully researching the spell.
Resolution. A character seeking to research a new spell makes an Intelligence (Arcana) check to determine whether they are able to successfully research the spell. The character gains a +1 bonus for every workweek beyond the first spent researching the spell, and a +1 bonus for every additional 100 gp spent on the research, up to a maximum bonus of +10. The monetary cost includes a modest lifestyle, so that you can perform your research in peace and privacy.
The DC for researching a spell is equal to 15 + the level of the spell you are seeking to research. On a success, you have learned the secrets of the spell, and may add it to your spellbook without paying any additional costs. On a failure, you may attempt the research again, but must begin anew in terms of both the time and monetary resources spent on the research.