1 POTS & CONTAINERS: Choose an overall design theme. Most people end up with various sizes of terra cotta pots scattered about on the patio.
(Terra cotta dries out extremely quickly and plant roots get 'baked' making it hard to keep anything besides geraniums alive.) This sort of 'eclectic' look works well in small gardens where there is plenty of greenery and shade but falls flat in a modern condo. There are a number of different and more modern containers on the market, if you really are committed to having a roof garden then consider having custom built, insulated planters made.

2 SOIL: Regular triple mix will never work; it's easily compacted and there are no worms to aerate the soil. A high quality container mix with a slow (preferably organic) release fertilizer and plenty of Perlite or Vermiculite is well worth the money.

3 DRAINAGE: If you have a large container, it's important that the bottom has 'feet' or at least some space for air to move and water to drain out of pots. This is especially important if the balcony above you overshadows your balcony. Lining pots with filter cloth will stop soil particles from creeping out through drainage holes.

4 WEIGHT: If you are undertaking a big project on your patio or balcony, make sure that the structure can support all the extra weight. Saturated soil and concrete or clay pots can really add a lot of weight.

5 PLANTS: Having a beautiful set of pots is fine but be sure to choose appropriate plant material. Perennials are worth investing in if your containers are deep enough to support new growth and are insulated or protected enough from wind and elements to ensure winter survival. There are a number of wonderful annuals to choose from. Balance your flowers with foliage - an everyday Boston fern looks beautiful in the right setting and requires little maintenance or sunlight.

6 FLOORING: Just as a beautiful floor increases the value inside a home, it makes a dramatic difference on a patio. Most condos have very generic concrete pavers, making for an impersonal and cold look. Simply installing decking over the existing pavers (be sure not to drill into anything or compromise the roof membrane in any way) makes a world of difference.
Aside from using wood there are a number of recycled decking materials on the market with different patterns, finishes and colours.

7 SPACE: Consider how you want to use the patio space; is it a place to entertain, to retreat to or a beautiful view from the office? Decorate outside in a similar way to decorating inside – candles and cushions soften a space and add a romantic feel, sculptures and stones can add a natural feeling. Any garden should reflect the styles and tastes of the people who live there; usually it's a place to relax the rules a little.

8 MAINTENANCE: Choose plant material that's easy to maintain. Bonsais may be gorgeous but can be tricky to care for. Flowering plants usually require the spent blooms to be pinched back to encourage continuous blooms (often once seeds are produced a plant's need to continue blooming diminishes.) Watering is essential and easily forgotten when the weekend cottage rush takes hold. If your patio receives full sun all day consider moving pots closer to a shadier area or having someone come by to do the watering for you.

9 CAUTION: A few final things to consider are factors such as wind: many city patios are prone to sudden gusts of wind or a constant breeze so be careful with lightweight plastic furniture. Candles left outside can turn into a messy pool of wax at the end of a hot summer day and terra cotta pots dry out very quickly and break if tipped over by wind or a careless foot - many types of pots on the market are made of polyurethane and won't easily break or split open in the winter when freezing temperatures hit.