Are you challenged with sloping land? The robust, gnarly branches and tenacious roots of these species make them splendid plants for helping to carry in earth, so it is perhaps a good idea to check for these traits on the wild shrubs already present within the place you’re planning your backyard.
So for carbon you can use dry plant matter reminiscent of twigs and lifeless leaves, sawdust, charcoal, straw (watch out with placing this close to the highest; if there are grass seeds present they will take over your garden) or even paper (although it depends on how long you might be planning to leave the backyard to ‘treatment’, as paper may not decompose quick sufficient to integrate with the rest of your soil).
I believe that for other than very small terraces a swale in the back of the terrace, on the foot of the wall, will have a number of advantages. The total gross exterior area of the three homes was roughly 1,000sqm, and given the high values within the area, that they had been designed with a view to maximising their value, with less consideration given to the ease of development.
Fastidiously dig out the soil from the top part of the backyard and transfer it to the ‘dam’ at the backside, smoothing out the bottom as you do so until the extent is kind of horizontal. Since you may be making essentially a curved ‘dam’ to hold the earth wherein you level out your terrace with, you may need to utilise already-existing shrubs as part of the walls of the dam.