While growing up, I've tried a variety of craft projects, and one of my favorites has always been making knot Rosaries. I find making knot Rosaries to be very condusive to silent prayer and reflection, and you can do many great things with the Rosaries you make.
Knot Rosaries are very durable (when made properly), they feel great while praying the Rosary, the Divine Mercy Chaplet or other devotional prayers on them, and they look very nice. So far, none of the Rosaries I've made and given away or sold have had any problems falling apart, even after a few years of use! As an additional benefit, they are not very hard to make, and the supplies you will need do not cost very much at all!
I've always purchased the nylon twine for my knot Rosaries from FNT Industries, as they offer a great selection of colors, sizes and lengths of cord. My favorite cord to purchase is #36 Solid Color Nylon Twine; you can purchase a 500 ft. spool (good for about 25 rosaries at 5 yards per Rosary) for only $8, plus shipping. You can purchase white twine and dye it yourself to make interesting color combinations (click here for instructions). You can also usually find a few different sizes of this nylon twine in a local hardware store.
You don't have to use #36 twine, but I find that the beads look best with this size (#21 makes a much smaller rosary, but it might be better for younger, smaller hands).
For the crucifix/cross and the Marian medal, you have many different options. For a simple cord Rosary, you can make both parts completely from the nylon twine. For a more traditional look, with a Miraculous Medal and a metal Crucifix, you can purchase them separately (usually about $1 per rosary) and affix them to the Rosary using special knots. See the section 'More resources' at the bottom of this page for more suppliers for these parts.
For instructions, I will refer to the PDF guide from www.RosaryArmy.com, but I will add some of the tips and tricks I've learned here.
Step 1: Practice Making Knots
It may seem very hard to make a knot at first, but after five or so, you'll get the hang of it, and soon you'll be able to make knots without even looking most of the time! The key here is patience. Keep working until you have made a few knots in a row on a piece of practice cord (about two feet long).
Follow RosaryArmy's instructions for steps 1-5, then for step 6, hold on to the first loop (the one that controls the tightness of the loop) and last loop (the one that controls where the knot is) of cord, and control how you tighten the knot by pulling a little on the first loop, then 'messaging' the last loop and the string, then pulling the first loop again, until you've made the knot almost where it needs to be. Then 'message' the knot to exactly where you want it using your thumb and index finger. This is VERY important for making evenly and tightly spaced Hail Mary knots.
To see what exactly I mean, I have provided a video (about 700 KB for speedy downloading!) which requires QuickTime 7 or later to view. To watch the video, click the 'Play' button.
Step 2: Making Your Rosary
RosaryArmy's instructions are very good for making a complete rosary, but I'll offer a few extra tips here, and explain a few things in more detail.
After making a hundred or so of these knot Rosaries, I've gotten into the habit of trying to pray the decades of the Rosary as I make them. If I am making the Rosaries for a certain purpose, I will pray with the intention of that purpose in mind, and perhaps reflect on certain aspects of that mystery that have to do with the intention. You need not say the Rosary while you make it, thoughsometimes, I simply listen to music or talk with some friends while making a Rosary!
Check out New Advent's guide (with Biblical verses for reflection) for praying the Rosary. There are hundreds of great explanations and guides for praying the Rosary, as well as many different books, booklets and pamphlets with meditations and reflections on the 20 mysteries. Search Google or look through a local Catholic retailer to see some!
What to Do with Completed Knot Rosaries
There are many things you can do with your completed knot Rosaries. You can give them to friends and family members as gifts, you can donate them to many different Catholic organizations (such as a local parish) for distribution to those who don't have Rosaries, you can donate them to www.RosaryArmy.com, you can give them to soldiers in the military, you can sell them for fundraising, you can use them to help evangelize...
The sky's the limit! The Rosary is a great tool for prayer and meditation, and it's an easy sacramental to make. Start making some today, and perhaps your love for Mary, the Mother of God will deepen as mine has!