Mansard roofs can be problematic for shingles when the correct shingle is not installed.  This client is worried that re-roofing with shingles is going to have the same issues and wants to get an estimate on standing seam roofing.  Both materials can be a great choice. OC Duration shingles are designed to deliver a strong bond on a steep slope and are an acceptable, more affordable choice than standing seam.  They are a high quality shingle with a canvas strip to reinforce the nail lines preventing shingles from pulling through the nails. Standing seam roofing is also an acceptable choice, coming in at over twice the cost installed.