Used Formula:

The number of Units/Floor Area X Cost per area = Total Estimated Cost of Proposed Project

Reminder:

At first consultation and initial discussion about the proposed project, this rough approximation with a considerable margin of error is made in the planning stage when there are no sketch designs or drawings. 

Even though you have a big or small project, it doesn't mean that it will be cheaper or expensive. It would be best to consider several factors such as the number of bedrooms, preferred design, materials to be used, how many floors, and others that will significantly affect the actual cost.