Building with 1x2s?

[3KillerBs]

My yard is fenced but I still want the coop to be predator-proof just in case, like wearing pants AND suspenders. If a raccoon tries to climb up the side, will it collapse on itself? That would be bad.

No, it won't collapse, not when well-braced like that design. Flipping is more likely -- IF you have very strong predators (like bear), or strong winds. You will want to anchor the structure to the ground if that's the case.