In this article we outline the model development planned within the joint project Model-based city planning and application in climate change (MOSAIK). The MOSAIK project is funded by the German Federal Ministry of Education and Research (BMBF) within the framework Urban Climate Under Change ([UC]²) since 2016. The aim of MOSAIK is to develop a highly-efficient, modern, and high-resolution urban climate model that allows to be applied for building-resolving simulations of large cities such as Berlin (Germany). The new urban climate model will be based on the well-established large-eddy simulation code PALM, which already has numerous features related to this goal, such as an option for prescribing Cartesian obstacles. In this article we will outline those components that will be added or modified in the framework of MOSAIK. Moreover, we will discuss the everlasting issue of acquisition of suitable geographical information as input data and the underlying requirements from the model's perspective.