re: trying to buy a house before you sell yours - need options\suggestions

You can write a contract to do whatever you want.

1) Make a payment to him in exchange for a six month (or some other amount of time) exclusive purchase window

2) Rent it from him

3) Present him a purchase contract with a clause that says the contract is null and void if you don't sell your current house by XX date

Is the house you are looking at on the market? How long has it been on the market? Is it likely he could sell it before you can get the other one sold?