Posted: 05/05/2014 at 10:37
Are you planning on building a raised bed with sides on this patch, to keep the soil in place? With concrete underneath you will need to consider how to provide drainage so the plants don't get waterlogged.
Rather than buy compost for this patch, I would buy equal quantities of topsoil and bags of farmyard manure - both available in bags from garden centres - this will make much better growing conditions long term.
Do you want to grow veg or flowers?
Is the area in sun or shade?