You should also consider what kind of armor you want to make, throughout history knights have worn many different kinds of armor. Going by the fact that you're asking for templates I'm guessing you want to do a suit of plate, if so then I'd research the time period and style of plate you want to duplicate. Not all plate armor was the same, there were many styles and the styles changed considerably throughout time from plate and mail where you have plates over mail to later full suits where the only mail was in the joints.
Once you have chosen the style of armor you want to make I'd recommend, as Cal has, making your own patterns and templates based on research and using paper and poster board wrapped around whoever is going to wear the armor. I'd also sketch out what you want your armor to look like in the end before you even start so that you can pre-cut your template before you start measuring to simplify things a bit so there's a little less cutting.