I tried another similar Step stool and found it would not stay together. This stay together.

I had not tested the capacity totally. It will depend on your print setting and material. I made mine with 4 outer layers 15% infill, using PLA. I weigh 240lb (109kg) an was able to jump a few inches.

I printed my logo in the side. This is not on the files uploaded.

After the printing,

1. Move the joints to make sure they are flexible.
2. insert the corners in the top. as shown in the attached photo. The first side will go in easy. The second side will need more force to get together. This helps the parts stay together. These pins have a flat side and will go together in a flat position (the top is flat with the side). When the sides are locked together, it will not come apart.
3. Snap the end “hinge” parts in place. the knuckle of the hinge goes outward.
4. use the small rectangular pieces to lock everything together.

There are 2 sizes of stools, 1 that will print on a printer with a 200mm (7.9in) max print size and a second with a 256mm (10.0 in) max print size.

Depending on your printer setting, you might not need support. Printed fine with it on my X1C printer.