Use a standard - science project backboard.
Created 12 slides. (Can be from your workshop slides)
Print those on a standard 8.5 x 11 paper. Easy
Paste 3 slides vertically ... So if you think of paper 8.5 inches as you paste it in landscape form ... Let's say 9 inches. You can easily fit 3 from top to bottom. That is 27 in. of the 36 in. The side panels are 12 inches .. that easily fits the 11 in wide paper.
You paste 3 slides on each of the sides
For the larger middle panel you can fit 2 across ... 11 in per paper x 2 is 22 inches easily fit in the 24 inches across. And again 3 fit up and down for a total of 6 slides in the middle.
Position the slides to tell the story from top left down the left panel ... to bottom right in the corner.