What are the exact specifications of a Tallis or Tallit?

I would like to make my own. Are there any maximium or minimum sizes? How much gold (or is any gold) required? Is there a prayer that one must say over a shawl, to make it into a Tallis? How many knots are required? I think the number is four -- one at each corner of the garment, though most tallis makers provide more. What are the requirements for the prayer strip? What is the meaning of the prayer? Where are these laws documented, to look-up properly? Does anybody know the definitive book or (preferably) online text, which defines the proper requirements for a Tallis or Tallit?