1 For an average sized 1,500 square foot roof, that works out to a total PVC roofing cost of $6,000 to $18,000. 2  While certain types of PVC roofing material can be installed over the existing roof, the old roof may need to be removed and disposed of at an additional cost of $1.00 to $2.00 per square foot. While certain types of PVC roofing material can be installed over the existing roof, the old roof may need to be removed and disposed of at an additional cost of $1.00 to $2.00 per square foot.