Monolithic structures are generally attractive to aircraft manufacturers since they allow for simpler processing sequences: integral machining replaces in such a case fastening and associated preparation processes. Such structures however display some drawbacks: on the metallurgical point of view, higher gauges lead to lower properties due to the quench sensitivity of the 7xxx alloys generally used; on the costing point of view, generation of a lot of chips can jeopardize the overall economics of the considered part, specially when dealing with high value alloys, like Al-Li. There are various ways to improve the cost-weight trade-off of such monolithic structures. One of them consists in developing medium to high gauge alloys better suited to integral machining. For example, 2050 Al-Li solution displays overall better properties than incumbent 7050-T7451 alloy, which, added to its lower density and higher modulus, can allow for weight savings. Usage of such an alloy can however be limited by the higher price of the material. Other cost-weight balance can be achieved through friction stir welding (FSW). In such a case, the final part can indeed be manufactured by welding two or three pieces of lower gauges. Weight performance is thus a balance between the better alloys performances due to the lower material thickness, and the loss of properties in the heat-affected zone. The cost performance is also a balance between the better material usage and the relative manufacturing costs of welding versus machining. The presentation will highlight some of the key points leading to optimised FSW structures using new advanced conventional and Al-Li alloys.