Inspired by this hanging garden from Homemade Modern to make a planter for our window sill. It cost around $15 in materials and only took an hour or so to make!
Lay out however many planters you've got. Measure and mark the centers for the holes
Drill the holes, making sure to keep the pilot bit straight up and down on your center mark. This part was a bit hard for me, I'd never used a hole saw and it was a bit tough. But by the 4th hole I had the technique down fairly well. I recommend watching a few youtube videos first.
I don't have much of a workshop, so I did it off the edge of my dining table.
Once the holes are all made, the only thing to do is to assemble the sides by screwing them together. Then just put in your pots and add some plants. Liz went the extra mile and painted the pots, they came out looking great!