is GPA registered ? from facts mentioned by you it appears builder is not owner of land . it has been bought in wife name and she has given GPA to her husband . on said basis GPA has sold flat to you
. since you have already paid Rs 10 lakhs cash insist that sale deed be registered in your favour . better contact a local lawyer before making further payment .
it is necessary for you to meet a lawyer personally , show him case papers and take his opinion . without going through the papers it is difficult for us to advice