Question about a building built by a 3rd party on my Father in Law's land

Hi,
My father in law owns a house and lot in Malasiqui outright.
My father in law allowed a person to build a building on his land in an open area.
The verbal agreement was that the person that built the building would use the building 'rent free' for a period of time, after which my father in law would own the building. We are assuming the 'rent free' total amount would equal the amount the builder spent to build the building. No time period had been discussed, but the builder wants a very long period (10-12 years) for payback 'rent free'.
We don't believe there are any written contracts.
Our concern is that the person will 'squat' on the land because he built the building there, or somehow over time take over the land the building occupies.

Reading over the land laws in the Philippines, I found the Rights of Accession, specifically
----------------------
a) The owner of land on which anything has been built, sown or planted in good faith shall have the right :

aa) To appropriate as his own the works, sowing or planting after payment of indemnity provided by law.
------------------------

Where do we stand?
What would a payment of indemnity be?
Do we have need for concern?
thanks so much for your help
David Smith
Perseviranda Q Smith

is the owner still alive? my recommendation is that you negotiate with the builder to to put the agreement in writing. if no agreement can be reached, you will have to file a complaint in court to to determine how long the builder should be allowed to stay.

or you can claim they are staying under mere toleration and you can file an unlawful detainer case to eject them

Hello, Thank you so much for the reply and for the advice. Yes, my Dad is still alive and he is the one doing all the decisions. We just wanna make sure they will not take advantage of my parents co'z they are old. We did mail the agreement we want them to make and I do hope everything will be fine. Again, thank you so much.