In this paper simple cost models that contain small number of items that will be used for estimating the costs of the contracts were derived. Twenty-eight contracts that contain large number of items were used in this study for the development of these models. Cost significant philosophy was used as an approach to develop the models. This study has shown that about 80% of the total cost of the project are contained within 20% of the items, these items are called cost significant items, and each item has a value greater or equal to the mean item value. These models can be used only for multi-story residential buildings. The developed construction cost model contains about 25% of the items while the developed finishing cost model contains about 23% of the items. The expected accuracy for both cost models is within + 5% and the achieved accuracy is within + 7%.