The best part of this project is, about half of the material you need, could probably be found just by walking to the end of your road.
1. An old door. (as mentioned before - in this city lined with skips - the one thing in abundance is discarded doors.)
2. (using the measurements of the door) pick up 2 x long pieces (to fit length of door) and 2 x short piece (to fit top and bottom of door) of pressure treated wood (at least 10 inches wide) from your local DIY store. They will cut them to size if you don't have a saw.
3. 2 x Saw Horses or Trestles. You could try and pick some up in your local DIY store or buy them online here.
4. A packet of L brackets (8 in total)
5. A box of screws
6. Roll of plastic painters sheeting (to line the box)
7. Compost/Potting Soil
and seeds of your choice
Fit the wood around the outside of the door and screwed it.
Then secured the inside of the box with the 8 L brackets.
Set up your two saw horses/trestles outside and place the box on top. Line the box with plastic sheeting. This step will help prevent the water from eventually rotting the door. For our water drainage hole, leave the hole open where the door mechanism would usually go and remove the plastic in this area.
You can always drill more holes for drainage.
All that's left is to plant your seeds - or if you have already started growing seedlings, get ready to transfer them into their new home.
But first things first.
Go out and get skip hunting.