Buying house with option for seller buy back by February 2019

[Aref B.]

I am looking to purchase an investment property with a good tenant currently in place. Purchase price is $56,000 with $110,000 ARV. The owner is selling the house to get funds to make an investment in a business. He is under the impression the business will generate enough cash within 3 months or less to purchase back the house. Here are the terms we have agreed to I am just trying to figure out how to structure this in writing if I can do this right and protect myself as well as the interests of the seller. I would appreciate any suggestions on how to do this.

Here is the deal I have worked out with the seller. 

I will pay $56,000 plus all closing costs.  The lease with the tenant ends February 1st 2020.  The seller will have up until February 1st 2020 to purchase back the house under these terms and conditions.  

Seller must pay me $56,000 + All Closing costs + Any repairs made on the house up to the date of re-purchase + $20,000 Profit and can at that point buy back the house.  He can do it anytime before February 1st 2020.  After February 1st 2020 the seller would lose all rights to purchase back the house under those terms and conditions.

I was thinking to just put some similar language in the addendum portion of the contract.  Would this suffice or should I hire an attorney to draw up some paperwork?  I feel this is a win-win deal for me and the seller.  If he doesn't buy the house back I keep a great rental if he does I make $20,000 in profit which i'm fine with.

Looking forward to the responses