Hello Joo and thanks for your post.
If you are speaking of new housing, the costs associated with the building of the home are far and numerous. So numerous, in fact, that it far exceeds simply the cost of the materials, the acquisition of land, the architects, the structural engineers, the building contractors, and the sales staff. Each entity that provides a service to the home--fire department, water department, sewer, utiltiies, school districts, trash, building departments, inspectors, traffic, streets, etc. is paid a fee for every home that a developer builds. These fees are not covered in the building permit, but in a series of fees passed to the developer for creating housing and "burdening" an area with residents who will use city, county and state services. In addition to the "hard costs" of building a home, a developer also have costs associated with obtaining building loans and hiring staff to provide services after the home is sold. It is actually quite a lot of expenses, so if you wish to know how much the average developer makes, the income (or, of late, loss) can only be calculated based on the location, the area, and the inventory sales rate.
And, by the way, developers do NOT pay 6 percent sales commissions to anyone. While a developer may be willing to pay the buyer's agent a certain fee (here in California, it's between 2.5 and 3 percent), the sales person representing the developer may only be making a salary or, if a commission, between 0.5 and 1 percent per sale.
In the past, the developers with whom I've worked were shooting for between 10-20 percent income from the sale of each home. In recent years, however, most are simply hoping not to lose money on the house when the sale is finally consummated. For more information bout industry averages, check with your local office of the National Association of Home Builders or the Building Industry Association (they are affiliated).
Grace Mroioka, SRES
Area Pro Realty
San Jose, CA