Collaboration Agreement with Builder

Hi I wish to enter into collaboration agreement with builder for constructing a house, wherein four floors with Stilt parking will be construted. Builder will take one floor and 25% share in Stilt parking in lieu of construction done by him and rest three floors and 75% share in Stilt parking of the building will be with me. We wants to enter into registered agreement, for that Builder says, Description of Document will be Article 23-A Sale Agreement, (Sale and Collaboration agreement), wherein he'll pay the entire stamp duty at the time of initial agreement, and at the time of completion of building, another Article 23-A Sale Agreement will be executed and his share will be transferred to his name and he is asking for Power of Attorney to execute Sale Deed in favour of any other third party of his share of one floor, right at the time of initial Collaboration agreement. My queries are :- 1. Should I go for Registered Agreement or Unregistered Agreement. 2. If registered, What will be the Description of Document. 2. If agreement is Sale and Collaboration agreement, when should i execute Power of Attorney. 3. How to safe guard myself, that he should not ditch in between construction, and should not be able to sell his floor, without completing the whole building. Thanks Naresh