Decent first attempt, bravo. It has been mentioned but it's really critical. You need WAY more ventilation
Have a look around here and you'll see some great examples. And yes, the nest should be low. Basically vents should be well above their heads as they roost, roosts should be higher than nests to prevent roosting and sleeping in the nests. You mentioned concern about enough room. The formula is 4sq ft per bird inside NOT including nests, 10 sq ft per bird in the run. Good luck!
Not nearly enough ventilation. It's critical in preventing frostbite. The nest box is really high. It's best to have that down low to discourage them sleeping in it.
I would love to see how the legs and roof are attached.