My concern would be traffic and weight. Public buildings are designed with thicker/wider and more numerous structural elements compared to residential buildings.
I believe the residential standard for concrete structures in India (where I am) specifies a minimum live load bearing capacity of 2kN/m2 (approx 200 kg/m2). This is much higher for schools/colleges/libraries/auditoriums etc.
Some one deleted their reply to you listing densities of paper and water. Here are some figures from Wikipedia
- The density of paper ranges from 250 kg/m3 (16 lb/cu ft) for tissue paper to 1500 kg/m3 (94 lb/cu ft) for some specialty paper. Printing paper is about 800 kg/m3 (50 lb/cu ft).
- Water: 1000 kg/m3
So they are not that far apart when you consider that the average bookshelf is often bigger than the average aquarium.
Cost: rent for a 2 bedroom apartment in a major metro, even split 10-20 ways, could still be a few hundred a month.
Permitting: Even if the apartment is zoned appropriately for a club or business, still need construction permit for the shelves/weight stored on them, fire permit for the storage of flammable materials, fire permitting/review for maximum occupancy, plus at least one other that won't be apparent until neck deep in the project.
Incorporation: Would be very, very wise to do this under an LLC (in CA, an extra 1000/year tax + minor fees and hassle)
Liability: Need insurance in case someone gets hurt (e.g. someone trips over a pile of books left on the floor)
Lease: Boiler plate leases will typically indirectly disallow this sort of endeavor (via guest limits or similar)
(This isn't even considering any library-specific laws or requirements, which presumably exist in at least some jurisdictions)
For that matter, the hacker space Noisebridge in San Francisco houses a large collection of data books and other often dated technical books. If you need to find the paper, they are a reasonable place to go and look.
Local governments and rich philanthropists helped spread the public library concept to be what it is today.