When I make rosaries of whatever type, Catholic, Christian, Buddhist etc..  I usually make a small bag to keep them in.  Over the years, I've experimented with different approaches and materials.  For now I've settled on mercerized cotton crocheted bags. There's a wide selection of colors available.  The cotton is durable while retaining a comfortable feel in the hand.

Disclaimer:  I'm no knitting/crochet expert, so these instructions are likely to be, shall we say, "nonstandard".    

Start with a skein of Mercerized Cotton and a 5.00mm hook.

(ignore the hockey-stick-like tape job on the handle..I have big mitts and it helps me to grip small diameter crochet hooks..)

Chain 13 loosely.

Turn

Insert hook into second chain from hook.

Single Crochet across. 12 Single Crochets

*Chain 1.  Turn.  Single Crochet across *

Repeat * until you have about a 6" rectangle.

Here it is after a few rows.

Finished length..

Without removing the hook, Single Crochet all around the outside of the rectangle, ending where you started.

On long sides of rectangle, Single Crochet in every end space.

Without removing hook,  fold rectangle to form the beginnings of the bag, taking care to leave enough material for a flap. 

Single crochet the front and back side closed  from top to bottom.

At end, pull through and cut, leaving about 6-8" of thread to work in later.

Close the opposite side of the bag closed by inserting the hook from back to front and Single Crochet from top to bottom.

At end, pull through and cut, leaving 6-8" of thread to work in later.

After this step, turn bag inside out.  This will hide the SC closing stitches and give the bag a more boxy look...

To finish the flap, insert hook from front to back into the first Single Crochet stitch above the bag opening.

Single Crochet around edge of flap almost to center of flap. (you'll have to eyeball this..)

When you are just short of the middle of the flap, make the flap buttonhole and buttonhole tab by:

Chain 2

Skip 2 Single Crochet

Single Crochet to end of flap

Chain 1.

Turn.

Single Crochet back up to buttonhole. 4 Double Crochet in buttonhole. (this makes the flap tab). Single crochet to end of flap.

Pull through and cut, leaving 6-8" to work in later.

Here's a back view of the finished flap showing the buttonhole and buttonhole tab...

Here''s the bag with the flap closed...

Now's a good time to work in all the loose ends.

Add button to front.

Done!