Determine your share in the property to be developed......50-50 or 60-40 or whatever.Keep all your title papers in order.Sale deed or any other deed conferring title on you.Municipal tax paid receipts.Whether property has been mutated in your name in case of partition or gift or inheritance.Discuss with Developer reimbursement of expenses for relocation during the Project period.Discuss liability of GST on portion alloted to you which will arise when project is complete and OC is issued.You can negotiate if he will pay....currently 5% of value of share .The registration value of first sale of any apartment by Developer will be taken as bench mark for all flats.Say he registers a flat to 80 L,the GST will be 4L.So you will have to pay 4Xnumber of flats alloted to you presuming all flats are same size.You will have to source funds to pay this tax.Since you are likely to avail LTGC benefits you cannot sell your flats for two years officially from date of issue if OC which is the date on which Capital Gains is reckoned to have accrued to you.It is a Catch 22 situation.Now consult a good lawyer who can really draft a pucca JDA.Dont go for standard templates which are cut and paste jobs.Even if the Developer gives the draft get it better by your lawyer to ensure that there are no onerous clause's affecting your interest as Owner.List out all the amenities Developer will be providing,quality of products,products by brand name or equivalent etc.Most importantly consult a C A to understand Capital Gains implications.I am writing this from practical experience,I am not a CA or lawyer.Good luck.