Three pieces crossways would 36' even before you trim for seams.Not 40.Interesting we just had our first quote that recommended in the large room instead of a 12ft by 40 piece and 3ft 40 ( in 3 pieces) he recommended Running 3 12ft pieces the other direction horizontal, with the room layout we would cross over 2 seams, not sure about that.
he said light entering room would then go direction of the seams.
It doesn't have to be waste. If you go back to post #9 there is a picture, looks like a couple of smaller rooms where smaller pieces could be used. We would need to see a dimensioned floor plan before rendering a final answer.So you would buy 2 12' x 40 ' and have a 8' 9' x 40' as waste?