Builder Leaseback

I am looking for some quick information. A builder is taking bids for the purchase of their model homes. They will lease back the homes for 18 months at 8% with the option of a month to month for an additional 18 months. I am unsure of what that means. Does it mean that they will pay an annual rate of 8% of the purchase price for the 18 month lease? Or am I way off? The bidding closes soon but if I don’t figure it out in time for this opportunity I will still welcome all information/advice for when the next opportunity arises. Thank you.