I have a customer who wants me to quote her on a new roof here in Iowa. The roof is aroung 20 square with two valleys and each part of it has a different amount of shingles on it ranging from one layer asphalt to 3 layers asphalt to 2 layers asphalt with one layer wood shake. Normally you would tear it all off and put on new shingles and sheathing as needed. But she wants me to quote her on doing steel too. Would you guys do steel right over the roof as it is or do a complete tearoff and then steel?Thanks for the advice.