Parking Sunday to Saturday
If I drop my car off on Sunday (am) and pick up on Saturday (am), what fee do I pay, is it the weekly rate of 40€?
Yes, you will pay the weekly rate, as it's cheaper than paying per day for six days - 40€ to 60€. The fact you don't use one day of the week you buy doesn't matter.
Whatever you do buy the weekly rate when you arrive at the airport. Don't wait until you leave after parking for six days. As then you will pay the daily rate!
Prices subject to change!