Pete,
to fit a curved ridge & straight sheets each side is a extremely time consuming job to get the shhets to corrigate, The curving costs are around $8.00/sheet, & curving iron is three times the cost of normal custom orb.
This procedure is not cheaper, in fact when quoting it is about double the labour costs.
However when done by a professional, it looks good & will give a better weatherproofing.
I would not suggest that a leyman attempt the procedure unless they were working with a professional skilled in curved roofing.
Bob