FM,
I am NOT a professional kiltmaker. I do sew and have made three kilts for myself. 4 metres is not a wise investment. In an ideal world the fabric would be cut perfectly square, in the real world it is not. I realize that the tartan is quite dear (expensive). For 6 metres you get a well made kilt and a well made fly plaid. There also needs to be some wiggle room to make the tartan line up where the splice is sewn so that the pleats look right, especially if it is to the sett. This is my two cents worth, as I have sewn two tartan kilts for myself using Barb's book.