I like the coop, and the idea of having a floor entrance for the chickens.
I would locate it in (picture-view) the closest corner to the viewer.
You can build a frame around the hole using 1x4 or 1x6 to keep the shaving in.
I left my entrance flush with the floor to make it easy to get the bedding out. To prevent bedding from falling out the door whenever I opened it (doors have to open out, btw), I put a removable running board in front of the entranceway.
Here are the updated pics of my coop progress. I completed the roof this morning. Still have to enclose the run, pain the whole thing and finish the roost. You asked about the pop door; I have it opended so you can see how It was trimmed. If you have any specific build questions PM me and we can exchange numbers or design ideas. I will add an auto door opener in the future.