Replace the concrete with the smaller size is not the right solution for small savings, not worth the resikona. The greatest savings is 'delete' activities 'loading plug' construction because we do not have a good design plan.
I noticed the condition of the client. If the client funds is limited, I will design the house with the concept of gradual construction. If the land is already an old building, the old buildings that I always try not dismantled in order to save costs.