In the last years, several robots for building façade cleaning have been designed and some prototypes have been developed. However, most of these robotics systems are too expensive to be introduced in the market or are only able to cope with very simple completely flat glass façades. Funded by the European Commission, a consortium formed by several European enterprises and research institutions is developing a semi-automatic low cost robotic system that is able to cope with the cleaning tasks of most of the existing large building façades. The robotics system is semi-automatic because one single human operator is necessary to supervise the robot task and to perform simple operations. However, this operator, located at the ground, increase the security of the cleaning task. The main specifications for a marketable robotic façade cleaning system are presented and after that, a first description of the proposed robot is presented, showing the concept of the system and the control architecture.