Functional layout of the building, understood as a layout or set of the facility rooms (or groups of rooms) with a system of internal communication, creates an environment and a place of mutual relations between the occupants of the object. Achieving optimal (from the occupants' point of view) spatial arrangement is possible through activities that often go beyond the stage of architectural design. Adopted in the architectural design, most often during trial and error process or on the basis of previous experience (evidence-based design), functional layout is subject to continuous evaluation and dynamic changing since the beginning of its use. Such verification of the occupancy phase allows to plan future, possible transformations, as well as to develop model solutions for use in other settings. In broader terms, the research hypothesis is to examine whether and how the collected datasets concerning the facility and its utilization can be used to develop methods for assessing functional layout of buildings. In other words, if it is possible to develop an objective method of assessing functional layouts basing on a set of buildings' parameters: technical, technological and functional ones and whether the method allows developing a set of tools enhancing the design methodology of complex functional objects. By linking the design with the construction phase it is possible to build parametric models of functional layouts, especially in the context of sustainable design or lean design in every aspect: ecological (by reducing the property's impact on environment), economic (by optimizing its cost) and social (through the implementation of high-performance work environment). Parameterization of size and functional connections of the facility become part of the analyses, as well as the element of model solutions. The "lean" approach means the process of analysis of the existing scheme and consequently finding weak points as well as means for eliminating these defects. This approach, supplemented by the method of reverse engineering means that already in the design phase there is essential knowledge about the functioning of the facility. It is far beyond intuitive knowledge, based on the standards and specifications. In the scope of reverse engineering methods, the subject of the research is an audit of the product (i.e. architectural design, especially the built spatial layout) in order to determine exactly how it works. Information gained in this way is to help building a system for supporting decisions for preparing design solutions for future investments as well as the functional analysis itself becomes an essential part of the setting up building information process. The data are presented with graphical methods as networks of different factors between rooms. The direct analytical method for the setting is to determine the functional collision between users' tracks, finding or indication of the shortest paths connecting analyzed rooms and finally to identify the optimal location of these rooms (each according to different factor). The measurement data are supplemented by the results of surveys conducted among users of hospitals, statistics and quantitative medical procedures performed in the test section of the hospital. The results of research are transferred and integrated with BIM system (building information modelling system), and included in the specifications of the IFC (Industry Foundation Classes), especially at the level of information on the relationship between the individual properties associated with elements (in the case of hospitals it may be information about the necessary connections with other rooms, access times from or to specific rooms, rooms utilization conditions, fire safety protection and conditions and many other). At the level of the BIM specification the model data are integrated at the BIM 6D (an extension of the model data with a range of functional analysis) or even BIM 7D (additional integration with systems used at the stage of operation and maintenance of the facility).