you could draw an outline plan of your space.then plot on the plan acompass point.as the sun goes east to west it should give you an idea of what you've got.as you say the garage will cast some shade but if your garden is south facing and the garage is at one side this will be either in the morning eastern side or in the evening western side.
one good idea is when you've time and a sunny day spend the day in the garden and see where the sun falls throughout the day i've done this and it's amazing how what you think is a shady spoy gets plenty of sunlight.
with regard to your cuttings make a list of the conditions they need as some prefer shade and some like full sunthen as you create your garden you can place them to suit.i'm sure all will be come clear.
also why not have a look at your neighbours gardens and you'll see how they have designed their gardens.