I bought a 4’ grind box in the past that arrived preassembled. I didn’t know this wouldn’t be. I don’t own tools or have the space to build anything which is why I didn’t just buy wood and build one myself but this wasn’t that much different than assembling an IKEA table or something. It would have been cool if the 2x4s were sanded and I had some issues with screws overlapping when following the marks (painted dots and drilled holes in other pieces) but it’s still very convenient to get the whole kit with instructions. I coated it with stain and sealer to keep it dry and hopefully deter termites.
I still would recommend buying if you don’t want to deal with buying saws, lumber and cutting everything yourself. You still need to go buy a drill if you don’t have one. Don’t even try doing it by hand with whatever screwdriver you have lying around.