The proportion means visual balance. In terms of rooftop garden design, it is the art of getting a garden to fit well within the place in a proportionate way. When designing a garden, the shapes provided get a more pleasant design than the unbalanced ones, and therefore you should bet on them. In this image you can see how a design with proportional shapes is more beautiful than one with unbalanced shapes.
All rooftop garden design start with a model that in theory can be as you want, however there are usually limitations such as difficult to build areas or elements that require a large space. Some believe that the right design is achieved with symmetry, but the asymmetry, in our most fashionable times, can serve as much as the classic. Regardless of whether a model is symmetrical or not, the forms that compose it must always be proportional.
A well-designed garden is a balance of masses and voids. To achieve harmony between the two, you need a model that is satisfactory by itself, leaving aside for now the own and exclusive disadvantages of rooftop garden design, you must think of it as an empty space that can be filled with any shape you want. And then check if it works in terms of masses and voids.