Recently, the discovery of ultra-thin quasicrystalline films reinvigorated the field of two-dimensional (2D) oxides on metals, and raised the question of the reasons behind the emergence of the quasiperiodic order in these systems.1) In this talk, we focus on a theoretical approach based on Density Functional Theory.2) The structure of these 2D phases can be described by specific tilings using a few elementary tiles (squares, triangles and rhombuses).3) Calculations point the exothermic formation of these systems, which interact quite strongly with the underlying metal support. A significant relaxation in the direction perpendicular to the surface alleviates the strain due to the lattice mismatch between the substrate and the oxide layer. The calculated and experimental Scanning Tunnelling Microscopy images are in perfect agreement (SrTiO3/Pt system). This confirms both the atomic model and the 2D character of the oxide formed. By identifying relevant parameters for the stability, such as specific electronic effects, this study opens a path to the discovery of other complex 2D oxide ultra-thin films.