What is carpet area, built-up area & super built-up area?

Carpet area is the area enclosed within the walls, actual area to lay the carpet. This area does not include the thickness of the inner walls

Inaccurately reported square footage is the subject of numerous complaints by home buyers. A small percentage of cases involve giving incorrect information, but a larger number of complaints occur simply because agents and sellers don't know how to measure a home's square footage.

How do you know whether the price of the home per sq. ft. you are buying is reasonable?

Though this seems like an easy question, it is not as simple as it sounds. Keep in mind that much more goes into the market value of a house than its square footage. For example, two houses next door to each other can have the same square footage. But one house can have two bathrooms while the other can have one bathroom. So the previous will cost you more.

What is meant by carpet area, built-up area and super built-up area?

Carpet area is the actual usable area of an apartment, office unit, showroom, etc minus wall thickness. Carpet area is the area enclosed within the walls, actual area to lay the carpet. 

This area does not include the thickness of the inner walls.

Built-up area is the carpet area plus the thickness of outer walls and the balcony. 

Super built-up area is the built up area plus proportionate area of common areas such as the lobby, lifts shaft, stairs, etc. The plinth area along with a share of all common areas proportionately divided amongst all unit owners makes up the super built-up area.

How can knowing the above terms help me in buying a flat?

This break up is extremely essential as builders can place anywhere from 65%-85% of the super built-up area as carpet area. That means, if the price is quoted as Rs. 1,000 per sq ft super built-up area, the carpet area could be anywhere from Rs. 650 per sq ft to Rs. 850 per sq ft. If this break up is not mentioned in the agreement, demand that the vendor/ builder mention it in the sale deed.