[hkhanna]

If it were me, I'd prepare a basic contractor agreement with an hourly rate. And as a retainer, that agreement would guarantee a minimum number of hours a month. You would commit to provide those minimum hours but will not commit to go above that. If you do go above that minimum number of hours, they pay your hourly rate.

For example, you charge $100 per hour with a $1,000 per month retainer, guaranteeing them 10 hours per month. If you and they agree to go above 10 hours for a particular month, you charge $100 per hour in addition to your $1,000 per month retainer.