Hi @will.nash,
Material wise, in highly efficient systems, low working strains (i.e. the unit deformation of the material at its allowable stress) is paramount: light strong materials are not all the same, for example carbon fibres need to lengthen up to 14.3mm/m to reach their allowable stress; while graphene reaches its working capacity at only 0.75mm/m: the same structure manufactured in both materials at 100% efficiency (if that was possible) would have 19 times more deflection in carbon fibre, and could eventually need massive oversizing to control deflections.
For highly efficient building structures with typical serviceability constraints, working strain is more important than self-weight.
Anyway, efficient building structures will be so light I’m not sure it will be worth it as yet: check above the self-weight of our structural floor, made in normal (current) steels and concretes.