Our office is on three floors plus basement.  Not a lot of square
footage, but a lot of categories to store by floor.

Basement: archived or dead project files, and drawers of information on
potential consultants.  Hmmm!  plus old accounting/office records.
Drawings are roll-stored in boxes and sorted by job number.  Old
presentation boards were stacked against the defunct boiler, until it
was cut up last week and removed piece by piece.  We just gained about
40 more square feet of space to store more stuff.

First Floor:  books and reference materials.  We have a nice
accumulation on lighthouses, the Parthenons, and various building
types.

Second Floor:  proposals and finished reports, sorted by a numbering
system only our office understands.  Usually, I can find what I need.

Third Floor:  CSI product information, and CSI technical information on
open shelves.  I started the latter arrangement when I didn't know where
to put specific references like Copper and Common Sense, Slate Roofing
reprinted, or Metals in Historic Buildings, plus all those photocopied
magazine articles.  This has been extremely useful and fairly easy to
maintain.  It's the technical books that I can't sort by this system
that I don't know where to put, except that they end up with books on
the first floor.  Only a few periodicals are all together, regardless of
how old, e.g. APT and Traditional Building.  Other journals become dated
and we recycle them after a few years.

Of course, I still have my personal stash of conference packets and
literature and business cards.  Under my desk are pieces from various
buildings, found objects, and replacement stone samples.  Teaching has
generated more stuff...  Mostly, I don't bring it home!

Ilene