to come out and build one. They're not hard to do and won't cost a fortune and a half.

It beats trying to pick a tractor up to put it in the shed.

My best guess is that they have the ones that come with the shed and not separate because they're attached while the shed is being built and might be harder to retrofit without the services of, you guessed it, a carpenter.

but if you already have that one just add some galvanized screws to keep it together and some water sealer to keep it from rotting though that should take a few years even w/o any sealant.

The other alternative to building one out of wood would've been to make one out of concrete with wood forms.