The first step would be to understand what a rosary is and how it is prayed. That should help to answer questions of how many beads you need and how they should be placed. You can find explanations here:
The next step would be to assess your own skills. If you have never made a rosary before, you would likely find it easier to make a string bead rosary:
If you are experienced at crafting jewelry though, a much nicer rosary can be made with beads and wire:
You may not need to know this right now, but if you find you like making rosaries and would like to make rosaries as a charitable endeavor, there are also knotted rosaries:
Once you have this information and decide which kind of rosary you’d like to make, the final preparatory step would be to assess the person for whom you are making the gift. Catholic men usually use rosaries made of dark colors such as black, brown, dark blue, or dark green. The primary color can be accented with a complementary color in a lighter shade, but the primary color should be suitable to the age and sex of the recipient. (For example, a young boy might like a rosary made of light blue with white accents, but a man generally prefers stronger, darker colors.)
Finally, the finished rosary should be blessed. You can either ask a Catholic priest to do so before presenting the gift, or you can let your friend know that the rosary has not yet been blessed so that he can arrange to have it done himself.