8x4 yes. My husband doesn't like the walk in coop style, thinks it's harder to clean. We're making coops we can rake out into a wheelbarrow or cart that fits under the coop. We're making our chicken set up in a large oval shaped area divided into 4 quadrants. We can keep 4 flocks or rotate as needed to improve the quality of forage by not letting them destroy the grass etc.
I see.
That 4' depth really is about as deep as you can go with a raised coop that's not a walk in or reaching everything gets to difficult.
Needing to fit a wheelbarrow under makes the 3' kind of necessary too. Maybe measure the standard wheelbarrow and see if you can drop the floor some giving wind less of a place to grab.
Will you still be able to reach in with a wheelbarrow in place?
I use a big plastic shovel and scoop the coop bedding into a big pot from a tree then carry that to the compost or put under my trees directly. The big 8x14 coop takes 20 minutes to clean and then put new bedding even with a few bossy hens telling me about their day.
It's nice to be able to be out of the weather while tending the birds or treating any injury or illness.
Also being a walk in it's much easier to get adequate ventilation in place.
Just things to think about before you build.