Landscape Designer - Mediterranean garden

We have an area which can be 25 mts x 25mts. In a fertile valley. A walled building is on the south end. We are looking for a walled/secret garden with an olive tree in the middle, ancient. The garden is to be full of water-friendly aromatics with shade and areas to sit in, informal planting to wind through the garden so that anyone in the garden meanders. Pleached olives or fruit trees on the walls would be lovely. Need a loose design to help us start. Can send more photos and details.