For large, heavy books there are a couple of ways to beef up a regular drop-spine box.
Like most people, I usually make them with double walls.
I also make a modified inner tray, so that both hands can lift the book when removing it. The book this is for is around 19 x 15 inches, and quite heavy.
For even larger books, a lift off lid is a good idea, so the box doesn’t take up so much table space when open.
Since this book will be stored flat, on a metal shelf, and the client intends to read it once a week, there is a a slide off bottom piece to wear out. Even a durable cloth, like this canapetta, can wear quite quickly when slid on and off the shelf, there is an example here. It is adhered by friction, and when it wears through the client can mail it back for a new one, much cheaper than a new box.