The key challenges to town gardeners are lack of space, prevalence of shade and exposure.
However by making a careful selection of plants suitable for the limited space available, you can certainly create another semi secluded 'room' in your garden.
Using trellis and fencing to best effect with the right climbers you can enclose and divide up your space to provide the backdrop for herbaceous borders, smaller shrubs or container grown specimen plants.
The right selection is difficult for us to help with and advise on unless we can see pictures of your garden space and its surroundings. So, please send them to us and we will happily try to advise.