As long as you had some purlins spanning between the bent steel tube and the building wall at reasonable intervals, perhaps 2'-0" o/c, you should be able to have a steel roofing product bent to the radius you need. If VicWest operates in your area they could give you an idea of which of their profiles can be bent in the factory and shipped, and they will also confirm to which radius is achievable.
For attachment purposes, might be easier to install several layers of thin plywood onto the purlins first, then an underlay, then easier to attach the roofing sheets, flashings, etc...