A storage shed is to be built in the shape of a box with a square base. It should have volume 150 ft^3. The concrete for the base costs $4.00 per square foot, the roof material costs $2.00 per square foot, and the material for the sides costs $2.50 per square foot. Find the dimensions of the most economical shed. (Hint: the total cost will be equal the sum of the costs of each piece.)