Rules and request about moving in together, I have concerns?

So my boyfriend and myself have decided to move into his house together (owned by his dad) We both sat down a few times going over what each will contribute financially and he said that I cover the cost of groceries which is fair and because its his dads home he will pay his dad the rent (which isn't a lot), fine. He asked me last night if id be willing to pay him some money monthly so he can put it towards the upkeep of the house as there is work to be done on it as well as some to pay the gardener. I feel a little weird about this because ill be putting money to fixing up his fathers house technically and if we break up then I dont get any of what i put in to fix it up. I asked him if id have a say with this money and he said yes but over all he makes the final decision on where the money goes to what of the house. Now this move will save both of us money as renting a place of my own is killing me.
Now as appreciative as i am that he has offered to allow me to stay with him, I also dont want to fix up a home thats never going to be mine and also didn't break the home but have to fix it?

Am i being silly since I am saving money at the end of the day or is it unreasonable to ask me to pay to fix someone else house?

Help :-)

Rules and request about moving in together, I have concerns?
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