What you need to calculate is surface area of the room.
SA = 12 * 10 * 2 (for the two 12 ft long walls) = 240 ft^2
SA = 10 * 10 * 2 (for the two 10 ft long walls = 200 ft^2
200 + 240 = 440 total square feet of wall space.
Each double roll covers 56 sq ft.
440/56 = 7.86 double rolls; you cannot buy a partial double roll so we need to buy 8 double rolls