how to make a raised bed?

We made ours by cutting 2 foot long wood posts (2x2 inch is OK) for the supports.  

We cut the length and width of the planks (in our case, we used decking) to the size we had decided worked best for us.  

Then we hammered the posts into the four corners and drilled the planks into these.  We had to ensure the beds were levels, so dug out/added the soil as required.  We then placed another post half way down the bed, in our case, we put them on the outside of the plank (the other corner ones were placed on the inside) and drill through to fix.  

They are still secure three years later.

Some people dig out the paths, to level off and use to fill the beds - we didn't have the luxury of this as we had taken over the plot in mid-summer when the soil was rock hard and by the time we could afford the materials, we had filled the beds with vegetables growing!  

There is lots of advice available online.  There is a good video on Gardeners World's website as well as Youtube:

http://www.gardenersworld.com/how-to/projects/creative-projects/how-to-build-a-raised-bed/271.html

Thanks, I'll have a look :-)