Diffuse emission in the outskirts of galaxies, such as stellar tidal streams, galaxy stellar halos and intracluster light, provides important constraints on the structure and evolution of the Universe. However, such low surface brightness diffuse emission can be up to thousands of times dimmer (>29 AB mag/[square arcseconds]) than the sky background at 0.5-2.3 microns. Unveiling this information-rich, but so far hidden, diffuse emission with the Nancy Grace Roman Space Telescope requires an accurate knowledge of any large-scale background gradients in images. The goal of our approved and funded Roman Wide Field Science (WFS) project, ROSALIA, is to build a large-scale (from arcminutes up to the entire field of view) image background reconstruction tool that will allow the preservation and detection of diffuse, low surface brightness structures in Roman Wide Field Instrument (WFI) images. We will account for gradients in individual exposures created by astronomical (zodiacal light) or instrumental (in- and out-of-field stray light, thermal background) sources. ROSALIA will be validated using end-to-end simulations of WFI mosaics, and will be available to the whole astronomical user community.