Does anyone have plans for a 5'x 9' cubby

I was contemplating building on a 5'x8' redtrailer but found a steal on a sturdier 5'x9'. After consideration I realized the walls may be more difficult to construct since a 4x8 piece of plywood won't work.
Does anyone have any ideas or plans for a 5' x 9' platform?
Your help is greatly appreciated
Does anyone have any ideas or plans for a 5' x 9' platform?
Your help is greatly appreciated