One of the major application for IoT technologies are Smart Cities and intelligent Buildings (IB). Development of smart devices and systems for IB allow important energy savings, better comfort for their occupants and improve security, among others. Implementation of IoT paradigm in Building Management Systems (BMS) improve and expand their capabilities compared with traditional approaches. For this reason, an appropriate selection of the architecture platform for IoT is required to meet the requirements of scalability, manageability and data storage and visualization. In this work, an IoT based monitoring system for ambient variables in IB is presented. Variables considered are temperature, relative humidity and carbon dioxide concentration. The developed system has proven to be efficient, versatile and affordable.