If you run an HVAC building load calculation and your roof load is 0, check to see if you have a plenum return defined. If you do, the roof load is included in the “Plenum” category in the system load. The roof load is not included in the room load at all.
Whether you have a plenum return or not is specified by the zone that the room is in. To check this, use the DM HVAC->Building Definition->Rooms->Edit Rooms command and select the room with 0 roof load. Press the “Edit” button to the right of the zone that the room is in. The plenum setting is in the bottom-left of the “Zones” dialog. If it is disabled, look at the zone above the current zone until you find the zone where the plenum return is set.