Wsalaam Fatima,
Definition of Storey is based on if a diaphragm is provided or not. So for cases, where there is a concrete moment resisting frame system, that has a steel truss roof, if the roof has sufficient horizontal bracing (which is normally the case or the structure would be unstable), then it will act as diaphragm, and you can consider that construction up to roof as one story and any extensions above as another storey.
Now for cases where you have concrete column extending a bit from roof and steel columns are used, in my opinion (I could be wrong as I am out of touch from seismic since long), you can simply your design by still assuming 2 stories, one till steel roof and other to top of new construction, and design the connection between steel and concrete column with using over strength factors. This is the most simple answer I could give you without looking at the sketch.
Thanks.