I was on the roof and was feeling the cool breez of the dawn. Suddenly a humming sound drew my attention to a building roof to my SE corner. I could not believe my eyes. A silvery tetrahedron shaped object was hovering over the building and at the same time it was emittimg a greenish light. First I thought it was something light display, but after 2-3 minutes the humming increased and I was sure that this is an unearhtly thing. After 10 min or so it gradually shifted its path and flew to the eastern sky.