The first thing I noticed: do people like wet books? The way a lot of those libraries are designed, all the books are going to be ruined at the first rainstorm.
The Library of Congress doesn't keep a copy of everything. It doesn't even try. I was shocked to learn this, as a child growing up I had been told the Library of Congress kept a copy of everything.
The ones in Canada usually have sloped roofs to block rain. It's enough.
Indoor ones obviously don't need it.