My advice now remember I’m in Canada, is it insulate walls and floors first , we used foam sheets. Then make sure to have cross ventilation,you must have a moving “ breeze”.
We created a nesting box/ roost withpoop boards all on one wall , save space . Nestingbox has a 2x4 among the top with sand on top . They sleep up there , you can’t keep them off nesting boxes so we made use of the space.
Make a plan , a list of all your wants and a list of needs....
Have fun , and also use screws in the coop because they’re easier to take out when you change your mind ( I just know this)