I agree with mallehk - this is a must. I mean flat roof is not something out-of-ordinary, it is a common case allover the world. How hard can it be to make it possible in AC? I know there are workarounds, but that is just an excuse. I keep modeling roofs from slabs, pavements from roofs, stairs from slabs and roofs, and so on - this is not BIM as I see it.
As a thought - maybe the composites could have a 'variable' thickness as an option for some layers in it? Then, if a roof tool would be introduced with a "flat roof" option, some layers of the composite can go with the slope, some with the ceiling and the one with 'variable' thickness just fills the gap in between?
This also give us a lot of other options, as when changing wall/slab/other thickness only the 'variable' part changes (especially with walls with variable thickness). This would look just like 'complex profile' behavior, I believe, just one would not have to make all those profiles.
A bit off topic, but mesh tool should also use complex profiles IMHO. Not talking that it itself should be updated and improved a lot. Modeling terrain is hard work in AC, while in the meantime some other applications has made this process a breeze nearly 10 years ago...