Are there any regulations on the size or setup of an office. I work in a (closet office) very small office. It is an office in a restaurant which is why it is so small, it is not a revenue producing space so it was made as small as possible. I am the bookkeeper so I spend the whole day in the office, but the managers come in and use it as well. The ceiling is quite high and we have shelves up to the top.

There might be requirements about providing the space with proper ventilation and safety exits, but to the best of my knowledge there are no laws specifying the size of the office. The employer doesn't have to provide an office at all.

If you are concerned, it's really more a matter of building codes than employment law. Those are very specific to each jurisdiction, and you'd need to check locally.