If you live in an apartment or high rise having access to any outdoor space is a real bonus.
A balcony can be a great place to sit and watch the world go by and a roof terrace a very relaxing retreat.
Look around for some comfortable but stylish seating. [Patio furniture]
If you are not afforded a tropical climate make sure that it will withstand reasonable wear and tear. Be careful of size, cramming in too much will become a nuisance, however much you loved it to begin with.
If storage is an issue some benches come with space underneath the seat, ideal for hiding away recycling waste or tools. Have a good look around before deciding what is best for you.
Once you have something to sit on the addition of some plants can really create interesting atmosphere. If your balcony is tiny perhaps a hardy perennial growing in a handsome container is all that it requires. [Container gardening]
Your chosen plants will have to survive the elements so avoid expensive exotic species. Often a good size specimen of a hardy plant displayed in the right planter will look just as good.
Consider how much sunlight any greenery will receive, a sun loving plant will soon become very sickly if it only ever sees shade. When planting up ensure adequate drainage as over watering is often the quickest way to kill anything.
A group of matching containers can be more interesting, there is also the advantage that you can move them around periodically.