I designed these (well not really designed), more cobbled together, when i was looking for uses for the off cuts of pallets that i didn't reuse for the climbing frame ive made.
So yeah it took like 30 mins per one. cost about 50p.
Step 1: Tools and ting.
I used a mitre saw because im lazy and crap at sawing wood straight.
16mm spade bit to make a drainage hole.
belt sander (again, because im lazy)
End of a pallet
piece of wood which can serve as a base