The most important part before carrying out the housing construction is to make an estimate of the Budget Plan (RAB).The Budget Plan has variations that vary depending on the type of building, land area, class of building, material to be used in the building. With so many variations, it takes a relatively long time to estimate costs to suit your needs. In this case, an information system for estimating the cost of development can be used practically .Therefore this study will discuss how to create an expert system to determine the estimated cost of development. The development of this system will be used by the Expert System approach .This system starts with determining the cost of using an inference engine as the center of decision making on the expert system combined with facts on the database with a knowledge base to get an answer. The method used as a reasoning process in an inference machine is a forward chaining method. The results to be achieved are a system that can facilitate the users (users) to get an estimate of the cost of building a house to live quickly, and easily that can be done anytime and anywhere without having to consult in advance with an Architectural Consultant services company.