Hi
I would price this job higher than your regular price for regular commercial cleaning works, - it is only one hour a week, who are you going to get to do it for such a short amount of time (I don't want to hear the answer that you will do it yourself even if you will, think as a larger business). This is outside work and therefore will cost more in terms of PPE. Don't forget your risk assessments when you are working in places where there are vehicle access you have to include the risks.
Fox