vegetable patch design
vegetable patch size
One of the first things you need to do when building a vegetable patch is to decide how big to make it.  There are two answers to this question, the short answer and the long one.

The short answer
It's my experience that, given the demands of modern urban living, few people can successfully manage a vegetable plot larger than a typical community garden plot.  Which is probably an area of roughly 2 x 3 metres (6 1/2 x 10 feet).  And even this size plot is too big for many people. So it's preferable to start off with a small vegetable patch and expand when you have the time and experience to do so.  It makes more sense to run a small vegetable patch well than a large vegetable patch poorly.

the long answer
How big a vegetable patch you can comfortably manage will depend on a number of factors, many of which will have nothing to do with gardening.  Below are some factors to consider.

perception of the amount of land needed to grow vegetables
There is vegetable gardening book by John Jeavons with the wonderful title of How to grow more vegetables than you ever thought possible on less land than you can imagine. I think this title aptly sums up the fact that most people drastically over estimate the amount of land that is needed to grow vegetables.  Worked efficiently a 2 x 3 metre (6 1/2 x 10 feet) plot will produce a very large amount of vegetables.

gardening skills level
The skills level of the gardener makes a big difference to the amount of time required to maintain a vegetable patch.  Experienced gardeners generally need much less time to work a small garden and can run a much larger garden than a novice gardener.  When planning the size of a vegetable patch always consider your gardening skills level.

WACT (Work and commute time)
photo of vegetable patch
How big a vegetable patch you can comfortably manage will depend on a number of factors, many of which will have nothing to do with gardening.
Most of us need to work to make ends meet, and this will greatly limit the amount of time you can spend working a vegetable patch.  However it's not only the time you spend at work but the time you spend commuting to and from work that you have to consider.  For example a person working a forty hour week who spends two hours a day commuting to that job will in fact be away from their house and garden for fifty or more hours a week.  Such time spent away from the home will greatly limit the size of vegetable patch that can be worked comfortably.

GAP (garden access potential)
Another important thing to consider is how much time in a week you can potentially access  your garden.  I don't mean the actual time you spend in the garden but the time you are at home and can get into the garden at short notice.  Some garden activities, like watering newly planted seedlings, don't take much actual time but do require you to be available to do them at regular intervals.  The amount of GAP time you have available will have a significant influence on the size of vegetable patch you can manage.

Other social commitments
To a varying degree we all have many other activities that we have to attend to.  Family functions, kids social activities to supervise, your own sporting activities, committees to attend etc... all need and deserve our time.  These other social commitments have to be factored into the equation when considering how big a vegetable patch you can manage .

The time people have to commit to running a vegetable patch will vary depending on their stage in life.  For example people with young children or those working long hours will have much less time for a vegetable garden than a retired couple.  If you have been running a vegetable patch but, because of changing circumstances, find yourself with less time for gardening don't be afraid to reduce the size of your veggie patch.  For that reason I recommend that vegetable beds be made out of more temporary material, such as wood or corrugated iron, which can be easily dismantled.