Hi Sudhang,
The extra perks that you get from builder varies, it depends on the popularity of the builder and his accomplishments. What you can do is to compare notes with other people and decide what is best for you. It is paid on the old carpet area. The corpus amount is worked out on the basis of Rs……..per sq.fts on the existing carpet area.
According to me, before you go for this kind of deal and investing huge for redevelopment, you should be aware of all the procedures and the paper work involved so that you are not misguided into losing that money that you have. I am not scaring you, but every member should have a proper knowledge if they have to want to do the whole thing on their own.