What are the typical documents for purchase of a flat?

Agreement for sale
The usual practice is to have an Agreement for Sale for sale of undivided share of land to the Purchaser. This gives the right of purchase to the Purchaser, subject to the terms and conditions contained therein. This document also sets out the extent of undivided share of land to be purchased.
Agreement for Construction or Builders agreement
This contains the terms of construction and also payment by the Purchaser. The specifications of the flat are set out in this Agreement. This is in the nature of a Works Contract. The Purchaser acquires ownership on completion of the contract and delivery of the flat.

Other Agreements like, Amenities Agreement, Car Park Agreement, Common Area Allotment Agreement are also entered into depending on the requirements and the structure usually devised by the builder.