I like rectangular boxes fur Ukes(not saying square ones are bad, I just don't care for the overall look), about 8-9 inches wide. Height and depth don't matter as much to me as they're mostly the same. With that width, I can build a Concert size Uke and have enough room to place a bridge without getting too close to the edge of the box which can affect tone. Tenor scales tend to be too long to accomodate a CB unless I go for an extra long neck.
I personally believe that there is someone at the Padron Company that is a CBG builder. Those boxes are so plentiful and come in about every size there could be (they could all stand to be a bit deeper though). I haven't found that I need a proper neck to body ratio like Dave. I've made all different length necks to accomplish what I'm looking for. Usually the boxes I like are rectangles that are about 9"X6"X1.75".