This paper deals with the conceptual stage of the design process related to civil engineering. Different types of design knowledge representation essential in visual aspects of a human-computer dialogue are considered. They comprise designer's drawings expressing forms, layouts and functionality of designed artifacts, internal graph-based data structures obtained automatically on the basis of these drawings and logic formulas extracted from the graph data structures. The reasoning mechanism based on the first-order logic enables the system to assess the compatibility of designs with specified requirements and constraints. The feedback given by the system along with visualizations of initial design ideas enforce the designer's constructive visual perception and creativity. The presented approach is illustrated on the example of designing an indoor swimming pool.