You could actually hold more than that. As long as you have the perch space. Always have more perches/boxes than you do birds, or they will get overcrowded and stressed. Which in turn, will cause you to have fly offs and disease.
Anyways, the rule of thumb for pigeons is 12x12x12. But I found that most homers are more comfortable in a larger box, around 14x14x14. Depth and length of the boxes is more important than height.
What kind of perches are you planning on using? You can use V-perches, T-perches, or box perches. For box perches, the cubby holes should be 12-14 inches tall and long. It doesn't have to be quite as deep, just as long as they can stand in there comfortably and not have their butts squished against the wall
The "floors" of the cubby holes don't have to be as big as nest boxes either. A 4 inch wide board is enough for them to just perch in.
T-perches are the easiest by far to make. Just cut up some 2x4s, 5 inches out from the wall, and stick'em on the wall. V-perches are the same as T-perches, just with flaps on the sides, making it look like an upside down 'V'. The droppings fall on the sides and prevent the birds underneath from getting dirty.
If you want to get the most perch space out of your wall, I suggest mostly or all box perches. That way you have barriers between each bird, using the whole wall, instead of having to space out the rows of T's or V's out to prevent fighting.
seems like you couldn't fit too many nest boxes in with that big?I have a row of boxes that size that is portable about 3ft.hi at the top that i was going to use for the chicken coop I already had 2 of these in the chcicken coop do you think I could use it for the pigeon loft?It has 4 boxes and they are 12x12 with a roost that runs the front of the row that are