Property Matter

Sir, i am from bhopal,madhya pradesh.Mere papa ne builder se ghar khareda h.par builder huma stamp paper me ghar ka agreement buna k nhi de raha hai.ek plane paper me notary ka stamp lagwa k aur 500 rupess k 2 tickets chipka k de raha h.kya aisa agremeent legal hoga sir?kya aisa agreement lena sahi hoga?pls mere help kare... Thank you