Maybe you can sketch what you are trying to describe, because open with no top *or* sides would essentially be a shelf?
There is no one right or wrong answer when it comes to how to design a nest box. Lots of people use "community boxes" which are not divided into individual compartments. A lot of what works for you and your flock will depend on what your birds like - some like the communal/open approach while others prefer more private space that is darker, more closed in and secure feeling.
Yes thatnks for the info and I was meaning like a community type box I built them along the wall.. they are open and the are basically 2×4 and they are screwed to plywood to make the bottoms but are sectioned into 12 by 12 in boxes