I made these with the same wooden crates that I made my kids holiday boxes with. I picked them up at Walmart for $10 a piece. I then used some of the paint samples we had leftover from picking colors to paint our house. I lined each crate with weed mat, but I also considered using a potting nest type netting.
You will need:
A wooden crate for each type of plant you plan on planting.
A staple gun (or nail gun)
Cut your weed mat to fit the wooden crate.
Staple the weed mat to the inside of your wooden crate.
Paint the outside of the crate (preferably with outdoor paint)
Fill the planters with potting soil and plant your favorite seeds.
Photos of my process below: