Does anyone have experience writing seller financing offers?

I’m looking to write an offer on a house in the Hampton Roads area of Virginia. The home does not qualify for conventional financing due to needed repairs. I’m looking to write a seller financing offer with a 2 or 3 year balloon after I’ve made the repairs. Do I include all the financing terms in the offer or do I create a separate mortgage document? Are there any forms on bigger pockets I can use?