Semi covered parking

At the time of buying the flat, why did you not ask the builder for parking?  Did he collect the charges for the parking area?  If he agreed to provide a parking area, you can file a case against the builder.  

If you are in Maharashtra and the parking lot was not mentioned in the original agreement, under RERA you have no claim for the parking lot. Whether the parking lot is saleable is another matter. What is the meaning of semi-covered parking? Open parking lots will be property of the Society formed or to be formed and the builder cannot sell them.

What are the terms and conditions of the "agreement to sell" whether it included parking or not ?

If it is included in the agreement and not provided approach jurisdictional RERA or Consumer Disputes Redressal Commission through a local prudent lawyer.