Define the Green field area & Brown field area? What is the difference?

A Greenfield project is one where you start with a completely undeveloped area and Brownfield is usually one that has had some development but to fulfil requirements of client prior to start of any activity. 

Prefabrication of civil precast foundations, piping spools in green fleld to make ready for construction in advance

A Greenfield project is one where you start with a completely undeveloped area and Brownfield is usually one that has had some development.

Green field: -

The main advantage reason to build a new facility rather than purchase or lease an existing one is that a new facility offers the maximum design flexibility and efficiency to meet the project's requirements. An existing facility forces the company to adjust based on the present design and new facilities are typically much less costly to maintain than used facilities. If the company wants to advertise its new operation or attract employees, new facilities also tend to be more constructive.

Brown field:-

The clear advantage of a brown-field is that the building is already constructed. The costs of starting up may be significantly reduced. The time committed to construction can be avoided in this case. In cases where the facility previously supported a similar construction process, then brown-field can be a real revolution for project point of view.