These are rules for building a character's own library and researching known or new spells; they are only for mages working on their own, with their own resources.  The following does not apply to guild members, since they have access to the guild's library and resources.  

Source: The Complete Wizard's Handbook

• Researching Known Spells
• Researching New Spells
  

RESEARCHING KNOWN SPELLS

LIBRARY COSTS

• Basic Investment: This one-time expenditure represents the funds spent buying scrolls and books necessary to assemble a mage's personal library. To begin a library, a mage must spend 1d6 x 1,000gp.
• Operational Costs: This ongoing expenditure is the expense necessary to update and resupply a mage's library.   This cost is 1d6 x 100gp (x # of weeks of research required).

For spell research, a library's usefulness depends on its monetary value, not its actual number of books. Value determines the spell levels that may be researched. (The operational costs correspond to the purchase of supplies; half this cost is considered to be new tomes, so over the course of research, the wizard's library value increases by half the operational cost.)  

As a point of interest, assume that a single research book costs 1d10x100gp, and that it takes 1d6 + 4 weeks to locate 1,000gp worth of books. (Therefore, a library for researching 4th-level spells is valued at 14,000gp and contains 14-140 books.)

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INITIAL PREPARATION

After the basic investment, the mage must spend preparation time before research begins. This preparation lasts a number of weeks equal to the level of the proposed spell, plus one. This involves basic reading and reviewing of notes, and preparing mentally and physically for the grueling task ahead. 

RESEARCH TIME

The minimum spell research time is 2 weeks per spell level. When the minimum period's over, the mage checks to see if she's discovered her spell. If she fails, she can continue her research and check again every week thereafter. 

Success chance = {30% + researcher's Intelligence + researcher's level} - (2x spell level)

The mage can increase her chance by spending more than the required money for the weekly operational costs. For every extra 2,000gp spent per week, the base chance increases by 10% (to a maximum of 70%).

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RESEARCHING NEW SPELLS

The following adjustments apply to the above procedures when researching a new spell: 

• The operational cost is 2d6 x 100gp per week. 
• The base chance of success is 10 %. 

Library costs, preparation time, and minimum number of research weeks are the same as research of known spells. The cost of increasing the base chance is also the same, but the maximum base chance is only 50%. 

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