Facade-layout synthesis problem deals with the allocation of an undetermined number of rectangular parameterizable panels over a rectangular facade surface. Requirements state that panels must not overlap, must be placed in specific supporting areas and must cover existing windows and doors over the facade. Due to the constrained constitution of the problem, constraint satisfaction and constraint programming come naturally as solving techniques. However, as most constraint programming environments use as arguments a well-defined set of variables, speculation about the number of panels to be allocated becomes a critical issue for its automation. On this regard, we present a two-phase solution : First determine the structure of the layout-plan and second, pass to a constraint solver a fully declarative model using such structure. We show that our solutions are consistent over symmetrical facades, and thus, can be used for early stages of architectural design. Our goal is to assist architects with a constraint-based support system.