check out the depth of field calculator online, it think the website is DoFmaster, or some such. Bear in mind that you only need to focus as far as the furthest wall, not to infinity. Assume your lens will be zoomed out to 22mm because anything shorter will simply make things better, and aim to keep your aperture in the f8 to f11 range rather than risk running into diffraction. You need a tripod, of course.