Sounds cool.
letting someone move in or use the house without losing control of it
Look into your local rental laws. Here, free access has very little protection for either party, if one party misbehaved. But it only takes one dollar a month to become a renter which gives both parties a whole lot of legal protection, rights, and responsibilities.
With some, we had a ritual the person would hand us one dollar rent, each month then we would give them one dollar as thanks for being lovely.
Personally, I found one dollar rental to be too low as the other people treated the property with disrespect. $100 (where the local rent for a space that size starts at about $1,500 and average out about $3,000 a month) is about right. It's enough that the place has perceived value and things are less likely to get broken. The rent can get put towards future improvements for the space or electrical bill.