Why not just over lay it with hardwood decking tiles such as Ipe (pronounced Epay) or massaranduba? These can be loose laid on paving supports to allow drainage and protect roof covering, the high quality ones look just as good as tiles and don't need treating etc. They're even heavy enough to...
This page helped me decide which system to go for (I'll let you work it out).
[advertising link removed, mod 9]
Gives a pretty detailed explanation of the pros and cons of both.
There aren't too many mansard roof pictures on the net at the moment (especially under construction), but there is one here; [advertising removed, mod 9] .
It's not exactly the kind you're talking about but it should help you understand the general concept.
It's not that unusual to see a...