Lots of things I thought would work didn't and my first go around was not 100% satisfying, but I got it to work the next time around.
My box size was 9 bottles by 7 bottles (28 bottles total) and measured about 26 inches by 22 inches.
Note that I will not be growing edibles in this box. The combo of pre-treated wood, plastic and food.... not a good idea.
Step 1: Supplies
Plastic Bottles!! Heavyweight is good.
Pen or pencil.
Paper for writing down measurements and for funneling soil into the bottles.
Wood - 1"x 3", two pieces as long as the length and two pieces as long as the width PLUS 1-1/2 inches.
Drill and bits (to drill pilot holes for screws)
Hardware cloth or screen (to fit size and shape of your box)
Landscape cloth or weed barrier (to fit size and shape of your box PLUS add about 2 inches all around).
Wood screws - quantity: # of bottles x # bottles (long enough to go through the width of your wood and penetrate at least 1/2 inch into the plastic bottle), and eight 1-1/4" wood screws to hold the sides of the frame together.
Screwdriver, a cordless power drill makes life a LOT easier.
Measuring tape and/or ruler
Plastic bottles all the same type. 32 (or any other even number, depending on the shape and size you choose).
Soldering iron that you don't mind messing up to make drainage holes (you can use a drill instead or heat up an ice pick)
Wire (my project used less than 50 feet). I used 20 gauge copper because I like the patina, the slugs don't like it and I thought I had some on hand, but I didn't.
Slim piece of sturdy (non corrugated) cardboard or a spatula (to tuck landscape cloth into crevices)
Potting soil appropriate for whatever you are going to plant and little stones for drainage.
Plants, seeds, cuttings...