Validity and format of a sale deed.

Kindly advice on the validity of the following sale deed: Flat located on 3rd floor Current stage of construction:1st floor slab level.(Photo on the sale deed depicting the 1st floor slab) Landowners have executed the sale deed. Further, Landowners have given development rights to a developer firm(a partnership firm of the landowners) Construction agreement executed by the developer firm in favor of the proposed buyers. Sale deed cost- Rs. 10 lacs- paid to the landowners. Construction agreement cost- Rs.20 lakhs to be paid to the developer firm. The sale deed reads: "Sale of partly constructed flat no. XXX measuring 1000 sq ft and undivided share of land measuring- 600 sq.ft. Possession of the flat is hereby transferred to the buyers". If the above sale deed is invalid, how can it be corrected? Any rectification deed to be done? The builder and the purchaser are friends. However, what actions can each take against the other?