I am trying to buy a house and need to write up a proposale how do I start it?

the total price is 15,000 I am paying 5.000 down and 314 a mth for 36 mths and he wants me to write up this proposal and i need help trying to word it. The intress is 8% and that i am willing to do over three years .I must keep insurance on the house and the taxes paid of course. so how do i write that up??????