there are three types of slabs you as a builder could use . 150mm slab , 200mm slab , 250mm slab , the important thing here is to kwn what cinda loads the slab wil be subject to and the span , meaning the span the slab wil stretch length wise.
150mm perfect for balconys and short span .
200mm perfect for balconys , rooms , toilets , and family rooms ( normal homes)
250mm perfect for spans over 5metres , heavy duty slab , this slab can realy be used for homes,office, and warehouses, store rooms , (ect)