It might appear that there is no reason to prefabricate any part of a building, and it would be more economical to simply assemble materials on site. This could be true if the structure is in a rural area, but the expense of operating within the limits of a city is often much higher. This is one reason steel buildings have become popular. Many of the parts can be fabricated and partially assembled elsewhere, and then they are shipped into the city for final assembly. It is a way of cutting building costs, and there are several different elements involved.
Raw materials for steel are expensive to mine, and the manufacturing process can be complex. Choosing the least expensive manufacturer often depends upon where they are located. If a steel building fabrication plant is nearby, it could cut the cost of acquiring the steel pieces needed for the project. Shipping can be a huge expense with any heavy material, so locating a fabrication shop in the area would be one way to hold down the overall price.
Labour costs are often one of the largest pieces of any construction budget, and they vary by location. People working in a city will have to live in the area, so they expect a larger pay cheque each week. Their costs for housing, food and even entertainment could be greater than people living in a suburban or rural area, it retaining good workers means paying a living wage. If parts of a structure can be fabricated and partially assembled in an area where living costs are less expensive, then the company will be able to save money over time.
Shipping expenses will continue to be a factor because steel is one of the heaviest building materials, but subtracting wages and possible savings on material can go a long way toward cutting costs. Each small amount of money saved will lower the overall cost, and a large steel building can come in well below the cost of any other type of structure.