In the old days before the industrial revolution, houses were built by the people who were going to live in them, with a little help from their friends and family, out of materials which were wrested from the forest. Today, all the building materials are made in factories and the average family couldn't build a home if their lives depended on it. For our modern building needs, such as concrete countertops or glass staircases, we turn to construction contractors who will do our work for a fee.
There are many different types and levels of construction contractor. A general contractor is the company that is overseeing the building of the structure. If it's a military or government structure, the contractor is known as a prime contractor and is usually the winner of a bidding war. Bidding systems are often used to hire contractors in the private sector as well. If it's just one house the general contractor might do all the work itself using its own employees. However in cases where the company is hired to develop a whole tract of real estate, doing all the work would take much more time than is budgeted and the general contractor must hire sub-contractors to assist them.
Sub contractors, when they are hired, are responsible for a certain part of the overall building project and are answerable to the general contractor who is in charge of the project. Sometimes the area of a sub-contractor's responsibility is all aspects of a certain number of houses, but much more often it is for one specific aspect of all the houses. For example, a sub contractor might be hired to install telephones in all the homes plus the accompanying wires.
In very large projects, such as the building of housing tracts or high rise buildings, there might be several layers of sub contractors. For example, a the sub contractor hired by the general contractor to do the electrical work might hire another sub contractor to handle installing the light fixtures. In most cases, the sub sub-contractor must be approved by the general contractor, but in others the sub contractors are left to themselves. This co-ordination or non-co-ordination among companies can make or break a project.
Large projects like these are usually overseen by investment companies but contractors are also hired every day by ordinary people who want to spruce up their cottagess or condos. Because there are usually no licensing requirements to become a contractor, customers must choose their contractors carefully. Often contractors get most of their work through referrals from previous customers who were happy with their work.