To find the dimensions of the storage room, we can solve the equation:
x^2 + 3x - 108 = 0
By factoring or using the quadratic formula, we can find that x = 9 or x = -12. Since dimensions cannot be negative, the width of the storage room is 9 feet.
Therefore, the length of the storage room would be 9 + 3 = 12 feet.
So, the dimensions of the storage room are 9 feet by 12 feet.