Hire a landscape architect to design plans for you to execute as you have time and money.

Are you going to do the work yourself or hire someone to design and install a garden? If you are doing the work yourself take it one step at a time. Literally. Create different levels for the back yard and steps that lead to the different levels. In the far corner of the yard have a focal point so that the neighbors yard is not the only thing you see. A pergola with a bench would be nice. If your budget allows, put a watering system along the fence and plant vines or roses. What is your climate zone? Where do you live? Do you want to grow some of your own vegetables? Creating a garden is lots of fun and Houzz is full of good ideas. Look at pictures of terraced gardens and raised vegetable gardens.

What are you trying to achieve ? Do you require outdoor spaces for entertaining ?

Steps down to the low area would be nice. I see a fire pit, swimming pool or pond in the low area. Wild flowers/shrubs along the fence. Theupper terrace area under the pine tree would make a nice patio area. An informal and inexpensive way to make a patio would be to define the patio area with stones and fill the patio area with wood chips making a seating area with patio stones on the flattest area preferrably in the shade. Looks like you need a few trees or tall shrubs for screening.

The best way to decide what to do is to draw a site plan. Indicate building locations, prevailing wind direction, shady areas, good views & bad views, sloping area etc. Then work from that to select spots for trees and sitting etc https://www.houzz.com/photos/naturalistic-stone-firepit-traditional-landscape-santa-barbara-phvw-vp~506890



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