boy i haven't looked at cloth diapers in years but when i was buying and using them they were HUGE! too small for a burp cloth? wow, how big do you want them? i'm sorry i just can't get my mind around a burp cloth bigger than a cloth diaper (the last ones i bought were 42" square) so you could fold them into a well padded diaper shape.
if you want them to be water proof you can purchase the same fabric as used for water proof bed pads at stores like Joannes. i hope to see pictures of these giant burp clothes.