If you always have your top off then any consideration on adding weather stripping or some sort of seal to prevent water / airflow / dirt? Is that even a concern for you?
Also are you thinking of having this made out of wood, steel or plastic?
If you'll be making this yourself the one thing I strongly recommend is to make a template for each piece. (An item the right size with all the holes in the right place, like a stencil almost) This way if you ever want to re-create it (Maybe start making and selling them to other owners
you'll have an easy time. I once tried to make a bookshelf and didn't consider templates, so each piece of the bookshelf was a 1 off custom and suffice to say, they didn't fit together very well.