(I will assume the measurement is in feet). The room in terms of square feet is 14 times 11 is 154 square feet. This is the amount of wood you will need. Look at the box of planks of wood. If a box has 20 square feet worth, then you will need 154 divided by 20 square feet or 7.7 boxes. Round off that number to the nearest whole number and you will need 8 boxes. Add another 10 percent for mistakes in cutting. You will basically need 9 boxes in this example.