I have a small (15 ft by 15 ft approx) upper terrace in my back garden
which is currently completely covered with weeds.

My plan is to make the area useable by next spring. I'm not sure
exactly yet what I'm going to do with it - I want to keep it
reasonably maintenance free, although I definitely want an area to
grow vegetables.

The area was cleared by the previous owners before I moved to my new
home, but the weeds have returned with a vengance. What can I do to
ensure that the weeds don't come back, and when is the best time to
take any action?

Thanks in advance for any suggestions.