Thanks, Russ! The top shelves will be reached with a small portable step stool. They won't need to be accessed very often. My client has arranged the books so that those on the top shelf will not be needed very often.
In a previous life I worked as a full-time skydiver and have over 7500 skydives, so I'm familiar with heights. Regardless, stepping onto that clear floor for the first time was still a leap of faith!