It will be difficult to make the coop so that nothing can climb it. Honestly, it takes very little for an animal to grab onto. The 'people door' jamb might well be enough, then a raccoon would just have to get a good enough handhold where the roof-overhang meets the sidewall to swing around to the opening and presto, no more chickens.
Also dogs and coyotes and foxes jump REAL well, and weasels/minks/felines are not bad at it either, not to mention that owls will fly right in that slot if it is left open at night. (If it is not left open at night, I do not think that the coop itself is what you need to be coonproofing, it's the *run*).
JMHO, trying to save you from costly mistakes (costly both in terms of $$ and in terms of chickens and aggravation)
Good luck, have fun,
Pat