I'm moving forward on the library project (year 2 now), and I figured I'd
toss the latest dilemma to the porch....

The library is an unfinished room, 28' square. I'm pondering order of
operations. The shelves will be built-in on all 4 walls.

the question is: should I put the floor (probably maple) in first, and
build the shelves on top of it, or build the shelves first, and butt the
floor against them?

The shelves will be secured to the floor (roughly every 38"), and I am a
bit concerned with restricting cross grain wood movement if I put the floor
in first. However, most of the places where I've seen built-ins, they are
built over an installed floor.

I'd actually prefer to put the floor in last, so I don't have to worry
about scratches, gouges, and such but then, with a span of about 26' I'm
worried about expansion and movement. With a span that big, will the floor
trim be enough to hid any movement? We don't use A/C, and we heat with wood
in the winter, so humidity levels range from 95+% in summer to 35%-40%  in
winter. I've had no problem designing furniture to allow for that, but I've
never done a floor...

Am I being overly paranoid?

thanks
-j