For this example, I am making a case for a Walther PPK/S BB pistol, and of course the book of choice for this clearly must be a James Bond book. Since this requires a hardback, I chose a book by James Gardner, which are far easier to find at the used book stores and less expensive than the Ian Fleming books; as an added bonus, the James Gardner books tend to be thicker as well. Even this was a bit too thin for the PPK/S, with it's fairly fat grip panels, so rather than cut up the book (which I also want to read first) I decided that I could just use the dust jacket, and make a fake book that was slightly thicker than the original, but that would still fit the dust jacket. This sacrifices some of the cryptic nature of the safe, as it will only look good from the spine, but since it's going to go on a shelf alongside the other thrillers, I think that's an acceptable tradeoff.
Step 1: Determining the Layout
The book safe is going to be built in two parts. The first part will be the book cover. In this case we're going to fabricate a new book cover out of cardboard, tissue paper, and duct tape, which will mimic the cover of the hardback. Then, instead of filling it with sheets of paper, we are going to construct a box that will hold the contents of the book safe. Determine the measurements for the outside of the box. With a hardcover book, the pages are slightly smaller than the cover, so when you measure for the box, keep that in mind and leave a little extra space on the sides.
In this example, I construct the box out of cardboard, because it's free and easy to work with, and is strong enough for the intended purpose. The box for the safe could also be constructed of a more durable material, such as high density fiberboard, or even sheet metal, which would allow it to be locked shut. That would be a good solution if you needed, say, a tamper-resistant safe for a firearm in a house with children; however, it's no additional protection against theft since the safe itself is highly portable. The security of the book safe relies on camouflage, and tricking a potential thief into overlooking the safe.
Step 2: Building the Fake Book Cover
The next step is to make sure the cover looks like a hardback. Typically a hardcover has a layer of colored paper over the heavy cardboard core, with a cloth tape of contrasting color applied to the spine, and overlapping an inch or so of the front and back covers. I chose a piece of colored gift wrapping tissue in a green color (the original book was a blue-green shade) with black duct tape for the spine. Gaff tape would be a better choice, as it doesn't have the shiny plastic surface that duct tape has, but I used what I had handy.
The paper was applied to the covers with spray glue, and carefully pressed down to get a fairly wrinkle-free finish. The tissue was then wrapped over the edges, glued inside the covers with a glue stick, and the excess trimmed off. A couple of pieces of duct tape were applied over the spine, wrapping around the edges and into the interior, to complete the fake cover. It doesn't need to look perfect, since it will be covered in the dust cover from the original book, but you should choose the best looking edge to use as the top of the book safe, since it will be partially visible sitting on the shelf.
Step 3: Build the Body of the Book
The top of the box is not really required, since the book cover will cover it, but I wanted to provide some additional security by having a cover I could latch down. As when we were building the book cover, I made use of an existing fold in the cardboard box I was using for my materials, and cut it so that it would fit inside the safe box. Gluing the top to the inside of the box gave me all six sides of my safe box, ready to partition to fit the contents.
Step 4: Add Partitions
The partitions should be lower than the sides of the box so that the lid will close; in fact, the lower the partitions are (as long as they'll hold things in place) the easier it will be to add the fabric covering later.
For more examples of fitting the case, see here for the "English fit" or partition style, and and here for the "French fit" style.
Step 5: Add Fabric Lining
Start out with a piece of fabric several inches larger than the box on all sides; in this case I am covering the entire inside of the safe, including the lid. Place the fabric over the opening, with an inch or two sticking past the nearest edge. Start pushing the fabric down into the openings, pulling fabric in from the other edges. Once you have everything pushed into place, make sure that there is some fabric overhanging all edges, and that the items to go in the safe fit securely in place. Repeat the process as needed until you feel comfortable with doing it, because once you add glue, you can't undo the process.
Apply an even coat of spray glue to the inside of the safe, wherever fabric is going to adhere. Start from the near edge and push the fabric down onto the glue just as during the trial fitting. You might want a rounded object, like the eraser end of a pencil, to use to push the fabric into corners. There will inevitably be some wrinkles, but if you pull the fabric out towards the edges and corners of the box, you can minimize them. Try to build up the excess fabric in the corners wherever possible, since it can easily be trimmed from there. Push any other wrinkles into areas such as the joints of the partitions, where the won't be in the way.
Now trim off the excess fabric along the sides. Don't worry about corners yet, just get the edges trimmed off even with the edge of the box. If there are wrinkles along the edge, just squish them up against the edge and cut them off flush. For the corners, get a sharp pair of scissors and just trim off the excess, right down to the bottom. Now get the hot glue gun, and peel back the edges of the cuts you just made so you can run a bead of glue up the corner, and press the felt carefully into the glue. For the wrinkles along the edges, just put a dot of glue inside the wrinkle, and press it flat to keep it tucked up against the edge.
Step 6: Attach Cover to Body
The back and spine side of the safe should then be glued to the cover. Don't glue the front cover down, because it doesn't pivot along the same point as the lid of the safe, and it will not open correctly if not allowed to move independently. A short length of heavy waxed thread of the type used for leatherwork can be attached to the safe lid, and used to wrap around a small screw threaded into the side to hold the lid shut. An elastic band, such as a hair band, would also work.