I'm in the process of benchwork planning. my decision is based on two choices; "open grid or l-girder". I'm working with a company called "mianne", I guess they are considered "open grid" but my concern is that they recomend that risers be built on the plywood top where as all the books recomend building on the joists. any help would be appreciated in pointing me in the right direction. note; room layout is 18X13 if thats important.