I built a new wood dog box last year and tried some things that seem to work real well. I love the movable dividers, I am going to build another one this winter and do it the same just add two catch dog boxes in front facing out to each side. Going to be better quality next time but this test model has done well.
Box is 3'deep x 6'wide x 2'tall, 2' tall is to short for my catch dogs next one will be 2' 6".
Box has 3 doors across the back.
The new thing is 3 removable dividers. I can change the set up real easy buy sliding out or moving dividers.
I can have:
1- 3x6 box
2- 3x3 boxes
3- 2x3 boxes
or 1- 2x3 with 1-4x4
It has worked great so far, a coat of paint and she is done. Only took 2 sheets of ply-wood, 5 2x4's, and some 2x2's.
Paul T