1) obtain no due certifcate from the builder
2) builder should agree for transfer of flat
3) tripartitie agreement can be entered into between builder , investor and you
4) it should be duly stamped and regsitered
5)check whether title of builder is clear and marketable and building plans sanctioned
6) if you so desire let sale sale deed be executed between builder and investor
7) wait for issue of OC
7) then enter into agreement with seller for purchase of flat by regd sale deed