It looks as though it will tip, but we have never had any problems in that regard.
I made this one out of 1x6 pine. I just glued enough together to make it wide enough.
I bought a sheet of 3/4 inch plywood and was able to make 4 of them from it.
I have attached photos of the layout with a 1 inch grid drawn over it. Just transfer it to table paper to make your pattern.
You may have to tweek it a bit to make thing fit.