There are a number of software programs that will allow you to design tapestries once. This is certainly a great option if you are a beginner and just want to create a design in which you can wear one. Be sure to find one that has a great interface and a large variety of designs. The most difficult part about this option is deciding on a theme.
If you have a particular design in mind, it would be best to show it to someone who can make the design for you. This is especially true if you are designing the tapestry for someone else. They will know exactly what type of design would go well with the general style of clothing that you're wearing. This is especially important if you are getting the design done for someone's baby.