RRoogI have a 20 year old home with 1 layer of asphalt shingles that are curling in several places. How do I determine if I should: 1) Repair the curling shingles with similar shingles ( I have some spares that match from the original owner of the home ); 2) Put on a second layer of new shingls over the house: 3) Remove all shingles and put on new shingles. THanks