Very often is necessary to use large spaces without supports in low floors in designed building where the construction system of the higher levels is completely different. In realized design for hotel building the authors of this paper have proposed prestressed structure made up two slabs and concrete walls as a I-beam web. It was formed the structure similar to box-section bridge beam. In this paper are presented and discussed the designing assumptions, parameters, the static and strength analysis results and the structure detailing. Based on the obtained results and experience from design process the conclusions was drawn.