The agreement between the builder and the buyer needs to be perused to see whether time was an essence of the agreement between the parties. The clause regarding delivery of the possession also needs to be perused for better advice on how to quicken the pace.
However, a case for deficiency in service can be filed against the builder before the consumer forum along with a direction for completion of the project within a specified time frame. Also, before going to the consumer forum, you can send a legal notice to the builder for the unnecessary delay been caused, etc. and give him a specified period wherein the builder must complete the project. if the builder fails to do it, file a case before the consumer forum.