In rapidly changing circumstances, the construction industry shows tendency to be more complicated and expanded and these changes are becoming the main factors aggravating uncertainty in straightening construction costs in the industry. The most important process in preliminary phase is calculation of appropriate construction sum and accurate estimation is required to accomplish it. Currently, local constructors draw up estimates by using the ‘per square meter’ calculation method or by applying of previous cases as they are. These methods become suppressive cause for making clear decisions by occurring errors in quantity survey in a way of data emission, replication and so on. Therefore, in this study, approximate estimation model of finishing construction shall be proposed to assist people to make prompt decisions in initial design stage. To develop this research, the existing quoting practices shall be presented and categorized by usage of space. To achieve this, information on performance, furnishings and unit price according to space definition has been collected in advance, which again enable ontology knowledge classification scheming database of space unit to be utilized and presented as knowledge information.