I love to hear about those who endeavor to make their own kilt accessories! My advise is to go into a Scottish shop and fondle a Rob Roy for while... I managed to make my first that way, then modified the prototype for the second version. There was mention of a book that has a pattern in it, but I haven't checked it out yet.
Perhaps the Glengary can be started the same way? Maybe deconstruct a low priced one and build it off that pattern?
Best of luck... pm me if you want some pointers that I learned the hard way!