Which is cheaper, a concrete roof slab or a structural steel truss with roofing?
That depends entirely on the spans and your local costing. In some places you will find the cheapest answer is trusses with concrete poured over Q-deck roofing. In other cases the concete is not needed and the insulation and roofing goes directly on the Q-deck. Normally the Q-deck is the cheapest by a good margin if your labour is expensive and if there is a early completion bonus like avoiding a high interest rate for your financing. Every situation is different. There are reasons why they are competing systems. If one was always clearly a better choice it would be chosen all the time and the other method would disappear.
