Want clarification on MOU to be made by builder for 20% pending amount

Need to purchase a flat, i am short in some amount say 20% , will get the funds after few months builder proposed to do a MOU with 20% of cost of flat ,in this case if anything goes wrong in the deal can i claim my money referring the MOU as a legal document. How the MOU should be also should it be notarised or without notary will do.