Instructions. Mesure the square footage of the structure you wish to demolish using a tape measure. Multiply the length and the width of the structure to arrive at its area, which is represented in units squared.For example, if your structure is 10 feet wide and 14 1/2 feet long, you will arrive at the sum of 145 feet. You will then have to pay for 145 square feet of demolition.View the structure and determine its number of floors and the building material it's made of. Additional floors will add cost to demolition, and various building materials will have different demolition costs per square foot.nstructions. Mesure the square footage of the structure you wish to demolish using a tape measure. Multiply the length and the width of the structure to arrive at its area, which is represented in units squared.