I am interested in making vestments. I do not at the moment, but in my interest I have found a place that offers the patterns for more traditional vestments and offers materials and suggestions for the making of fine liturgical vestments.
sewvestment.com
This site is run by sisters in schism, sadly, but it does offer some wonderful advice, materials, and patterns. On the seminar page it says for the seminar, to make the vestment, one would need:
So, perhaps this above information will give you an idea of how much material to send. I would say about four or five yards is a good amount. You may want to think about sending a yard or so more just in case. And if it is too much, then they can use what is left to make the good Fr. something more too.
I do hope this information is helpful. God bless you for desiring to help!