Life Time Lease/Estate

[Mary Pierce]

I built my home on a family members property-guest house.  The family member and wife recently divorced and the their house and the guest house were put up for sale.  When I built my home they signed a notarized statement saying my husband and I had rights to the home we built till we died/passed away.  I was told I needed to record this agreement, which I intend on doing.  My question is, how do I figure out how much the guest is worth, in a rental aspect and how long to estimate life expectancy of my husband and I.  We want  to come up with a fair amount for a (buy off from the (relatives/sellers) when the home is sold.   We invested (150 Thousand in the build) of our own money, not including upgraded flooring, and window covers, which the contractor did not include.  The agreement is signed by both parties, who are now divorced.

Thank You