Mark,
I suggested, I think in the On Center forum, that the grid could be 1' X 12' and set Quan1 to be Tile Count (Visible). Then the "count" would be LF of roll to the next full foot. Quan2 could be Area and the difference between that and the Tile Count times 12 would be the off fall. I don't now how to use that in another room. But, you could create a new condition called "Off Fall" as a plain area condition the same color as the grid condition and place the area in another room that gets the same color carpet with the LF of the first roll by the width of waste as the area. Then when you takeoff the rest of that room put new carpet (grid) in the balance of the room only. It would take some time to move off falls around different rooms to get the best fit in a building. I've also seen specs that call for no seams in rooms less that 12' wide.
Flooring contractors have a program that lets them move the off fall to another room and re-use it.