how much to pay a contractor monthly for maintenance?

I have a rental property which is 100 years old, 1200 sq ft and 3 bdrm and 1 bath. the rental fee per month is $700. I want to hire or cooperate with a contractor (Chinese also). I am thinking to give him 1/7 (14.3%) of the rental fee per month, and in return, if there is any maintenance issue, he has to fix it for free. I will also be responsible for the material cost, he just does the labor. Is the fee too high or too low? How much is typical?