If the delay is inordinate without any valid reason you may first issue a legal notice to the builder to handover the property at once and to pay penal interest till the time he hands over the same from the date of assured period for handing over possession.
RERA has taken steps to not only make the promoter accountable but also make them pay compensation and penalty in cases of default of any provision of the rules.
In case the builder defaults and delays the possession of the property as per the 'agreement of sale', the buyer has the right to claim the refund of the amount paid along with interest.
Even in the case, the promoter's registration is cancelled, the buyer will have the right to a refund.
The interest percentage and the compensation amount (to be mentioned in the agreement of sale at the time of booking) in the case of any default could differ state-wise.
"The state governments are vested with the powers to fix the rate of interest in the case of any defaults by the builders. Each state government is required to notify the applicable rate of interest in the case of defaults in its rules and regulations under the Act.
Hence, the rate of interest may differ from state to state. ..