My husband and I wanted to build a raised planter box to use for growing vegetables as we live on a mountain and our soil is mostly rock and clay.  We also had an old ground-level deck in our back yard that we wanted to dispose of.  We cut the deck into five large pieces:  one for the bottom of the raised box and four for the sides.  We reused many of the old nails and screws as we could.  We even used an old tarp to line the sides of the box to keep the soil in.  We also lined the bottom of the box with a piece of screen we had in our garage so water could drain from the box, but the soil would not slip through the cracks between the planks.  The box did not cost us anything.  Our only cost was for the soil to fill it.  We look forward to planting vegetables in a couple of weeks.