There are plenty of tutorials on how to make a secret compartment in a book. However, usually it involves patient cutting of the pages with a knife. I do not have enough patience to do that, so I invented a method that I'm about to show you.

Supplies

An old book.
A couple pieces of plywood or hard cardboard
A bit of saran wrap
Wood glue

A Drill
A Jigsaw
A few clamps

Step 1: Find a Book

Find a book that would be thick enough for your needs. You may want to visit thrift shops or garage sales. Maybe you could use an old telephone book.

Step 2: Protect the Cover

Use food wrap to protect front and back covers along with a few pages at both sides.

Step 3: Glue the Pages

Use water diluted paper or wood glue to glue the pages so they wouldn't come loose.

Step 4: Apply Pressure

Apply pressure to the book and let the glue dry out.

Step 5: Compress the Pages

Use plywood or cardboard along with clamps to compress and protect the pages.

Step 6: Mark Guidelines

Mark guidelines to ease up the cutting process.

Step 7: Cut a Hole

Drill a little hole to insert the saw and using a jigsaw cut a hole. If your book is thicker than the length of your saw, repeat the cutting procedure from another side.