As staad pro capable to suggest and optimise steel member size, similarly staad should also be capable to suggest and optimize RCC members' section sizes, like beams, columns,shear walls, slabs, slabs etc. so that manual efforts would be minimised, time saving, efficient and economic design. Also software deliverables will be more.
Thank you for posting you idea. What logic are you prosing that STAAD.Pro should use in determining the size of concrete beams/columns/slabs? With steel members a profile size can be tested and maximum utilization determined, if above unity, then a larger size can be selected. If less than 1, then a smaller size selected. However for concrete this logic cannot be used as the design capacity is down to the rebar and it may be more rebar in a smaller size is better than less in a larger one. Other times it might better the other way round with a deeper beam and less rebar. This is why a good engineer sets the size of the members and checks that a good rebar arrangement can be made to fit it.