What is the service charge of a designer ?

I am plannig to do our courtyard landscaping.I want to know how much will the design alone cost ?Is the calculation done on sq ft basis ?We want a lawn,flowering plants and a walkway,area is 1500sq ft.Pls help.Our area has diffused sunlight,which flowering plant is ideal ? Which type of lawn is good ?|||The design will cost what the designer charges. We are not psychic.|||I would ask for a fixed price quote and a very clear written description of what they intend to do. That will give both sides of the contract the best chance for happiness.