Systematic climate change can may bring about abnormally heavy snowfall in wintertime, which means that roofs in exposition, municipal, industrial halls and sports arenas may be excessively and destructively loaded [Kłosek and Prószyński 2008]. Ten years have passed since the greatest construction disasters in the EU countries happened, when a whole series of grave accidents took place due to snow and ice overload of roofs in large halls. These events emphasize the need to introduce an early warning system to prevent that kind of risk. A geodetic system that moni- tors selected parts of structure can warn about a danger related to accumulation of masses of snow and about a degree of deflections in a building structure. The article presents the newest original measuring Multi-Disto Monitoring System (MDMS) for collecting information on current state of geometric deformation of steel or ferroconcrete gird- ers supporting large hall roofs.