Extended defects such as interfaces and grain boundaries play a fundamental role in material behavior, from manufacturing (e.g. precipitation hardening, sintering, additive manufacturing) to degradation during lifetime (e.g. creep, corrosion). Thus, understanding and controlling interfaces and grain boundaries is of vital importance for materials property prediction and design. Simulations can provide a means to obtain interface properties for which experiments can be challenging. Developments in simulation methods such as machine-learned potentials have increased the capability to model extended defects and polycrystalline materials. However, the construction of atomistic models of polycrystalline materials, grain boundaries and interfaces for simulations can be laborious without proper tools. This presentation demonstrates the microstructure and interface building capabilities of the MedeA software environment, highlighting new functionality. We will focus on the Microstructure builder, a tool for building polycrystalline structures and on the Interface builder which has been updated with the capability to generate high-symmetry grain boundary models. We will demonstrate those tools during the presentation and provide examples of how generated atomic models were used in material property prediction.