Looks great!

But consider this....

Dogs are denning critters by nature. A small volume, insulated DH will be heated by their own body heat in the winter. This will become more important when they get older. A chunk of old blanket for a door keeps the heat in remarkably well and can be removed and washed. Set the doorway threshold above the floor about 10" to allow for cedar chip bedding to keeps the fleas at bay. Locate the DH doorway on the leeward side of the prevailing winds. A roof and/or plantings on the south side of the run would provide summer shade.

F'ing engineers. PM for structural drawings & details....