Mimar Sinan served as the chief architect from 1538-1588 in the Golden Age of the Ottoman Empire. He was responsible for the design and construction of over 470 buildings of different sizes and functions. Unfortunately, Sinan’s methods of shaping, sizing, and construction are unknown since no records of his design principles have been found; however, the simultaneous construction of many buildings throughout the empire suggests that he used a common method, especially in the design of simple buildings of similar size and shape. In this study, Sinan's design principles were investigated in one of his small mosques, the Ferhat Pasha Complex in Çatalca, Istanbul. In the first phase of the study, the compatibility of the examined building’s plan with the methods known to be used in different civilizations, like quadratur, golden ratio, grid system, etc., were investigated, revealing that the sizes, forms, and locations of buildings are in accordance with a modular grid system. In the study’s second phase, the stages in the emergence of building design were shown by the inductive method. This system also played an important role in estimating the cost of the buildings and tracing the outlines of the plans to the ground.