While you're designing this, give yourself a little more roofing overhang over the front door and attach it so that it whisks water and/or snow toward the back side and doesn't bore a hole in the ground at the doorway. You can dig a trench in the back, filled with gravel to deal with water issues from the drainage in the back of the coop without it being inconvenient to walk on OR lay the gravel on the ground without a trench if digging one is too much like work. A flat roof (slanted towards the back) might be easier to build than this curved dome and would give you more play in how you set up the feed, water, roosts, nesting boxes etc. inside. Add a couple sheets of roofing on the sides to make walls; I like zinc as it tends to repair itself from small nicks and scratches through it's natural oxidization process.