Measure your palet, try to find two groups of boars that equal in width
Use your saw to chop the pallet down to size, watch out for your fingers.
Cut four pieces the same height for the ends.
Join the end pieces together wit some screws.
More screws .
Attach the bottom piece.
Line with some plastic, so it doesn't leak water all over the terrace.
Fill with potting mix.
Add some plants, like snow peas and parsley.