Alright. Building anything is COMMON SENSE. If you can't figure out the basic structure of a rail or box you need to think before you type. Honestly. I built an 18 foot dragons tail rail (6 feet tall) completely out of wood without any plans whats so ever. A box entitles 4 long supports going length wise, then several supports vertically. You you will also want supports side ways (horizontal) on top and bottom. Then on the interior you may want diagonal supports so the box doesn't fold under you. Then on the top you will want plywood to support any top sheet. Really now. If you have to ask about building something so simple, do you really think you should be building anything at all. THINK BEFORE YOU TYPE!!! ITS A BOX! DRAW A BOX, BUILD. NOT HARD