The digitalisation of the construction sector could potentially result in the creation of more efficient structures, with lower material wastage and improved worker safety. Current strategies for automating the construction of steel structures regard metal 3D printing processes, and in particular wire and arc additive manufacturing (WAAM), as an opportunity to build a new generation of efficient structures using less material. This, though, requires advanced multidisciplinary knowledge in manufacturing, metallurgy, structural engineering and computational design. There have been recent efforts to combine computational design with current digital fabrication procedures to realise efficient steel structures for the future. This chapter aims to provide insights into current research into and applications of WAAM in construction. It is based on preliminary results from new structural optimisation theories, the fabrication of large-scale elements with WAAM and structural verification of the first prototypes. The ambition is to increase the application of metal 3D printing in construction, through the development of a new generation of efficient beams and columns.