Sadly, there aren't any templates specially for creating custom UIs. You'll have to get a copy of one of the in-game UI's components ( a UI is divided in to 4 sections ) by using warcraft 3 viewer or a program that can view the mpq files, then use it as your "template" to make your own UI.
p/s: check out my custom ui list sig to see whether any of those UIs suit your needs.