In which the party does some research

 A few months back, quite early in this campaign, the party found themselves in a large village with a small "library."  They were seeking info on a specific type of demon and on silver smelting practices.  I was completely unprepared.  I set a CR in my head, let them roll.  They failed and it was unsatisfying for all.   

Did a little research of my own and stumbled across the Pathfinder rules.  Modified them a bit as follows and we'll see how they work in practice.

All libraries (personal and public) will have a stat block which includes the following: a CR, a Complexity rating, which reflects the intricacy or confusing nature of the library’s contents, a “language,” a research check based on the knowledge contained therein (based on relevant skills with insight or investigation for general knowledge.) Some libraries grant a bonus on Research checks based on the nature of that library’s collections. A library’s Complexity rating serves as the DC for Research checks that attempt to unravel that library’s clues.

Library research is done in an 8 hour block. An assistant can reduce that block to 5 hours and a second assistant can reduce it to 3 hours. After the time is spent the researcher makes a Research check. A successful Research check reduces the library knowledge points (think hit points) by 1, plus one for each 5 over the required roll. Reducing kp to 0 concludes research in that facility and grants XP to those doing the research.

Example: Morigan the fighter and Kona the ranger go to the small library in Crysrift (population 2655) to research the “demon” they are to confront in the wilderness. This small “collection” has a CR of 2, a complexity of 10 and a mere 3 kp, mostly in the area of local knowledge, animal handling, nature, medicine and survival. Kona brings a +3 insight bonus. After 5 hours the RC is rolled. Anything over a 7 would reveal knowledge but as the area of research isn't really covered no information might be found. A roll of 17 or greater would reduce the kp to 0 and disclose that everything that CAN be learned here has been learned. 

 Edit to add:  Building a library!

 1.  Nature of the collection.  Most libraries will have at LEAST local info.  Roll a d10 for every 10k people and add an area of knowledge.  If you roll a six PICK area, AND roll again.  Any time a subjecy is RE-rolled, add an "area of concentration.

1. Arcana (ancient mysteries, magic traditions, arcane symbols, constructs, dragons, magical beasts)
2. Dungeoneering (aberrations, caverns, oozes, spelunking)
3. Engineering (buildings, aqueducts, bridges, fortifications)
4. Geography (lands, terrain, climate, people)
5. History (wars, colonies, migrations, founding of cities)
6. Local (legends, personalities, inhabitants, laws, customs, traditions, humanoids)
7. Nature (animals, fey, monstrous humanoids, plants, seasons and cycles, weather, vermin)
8. Nobility (lineages, heraldry, personalities, royalty)
9. Planes (the Inner Planes, the Outer Planes, the Astral Plane, the Ethereal Plane, outsiders, planar magic)
10. Religion (gods and goddesses, mythic history, ecclesiastic tradition, holy symbols, undead.

2.  Establish CR. It's the level of the highest member of the party

3.  Determine complexity.  Base CR + 10 + 10%  rounded up .

4.  Calculate Knowledge points.  Complexity * 3

5.  Make sure there's time pressure

6.  Establish research thresholds.  If kp < 25 there's info every 5.  If kp>30 there's info every 10.

Example.  Current party goes to Capitol City.  Library collection includes all ten areas.  CR is 7.  Complexity is 20.  KP is 60.  We'll need 5 steps of information.