there is another mf tread that talk about that seo problem..
i run into the same seo problem but if i dont recall well it was cuz the two elements didnt have the same material applied to it.....i think !!
i have done it in mf in a different way: with bplines i have "formed" surfaces/planes using the loft or one of those tools and then extrude for the thickness.
but it seems that your roof doesnt need mf...profiler probably would do
MACBKPro /32GiG / 240SSD
AC V6 to V18 - RVT V11 to V16