Having assembled 2 coops,and then having to modify the smaller of them,as it was that small,I can attest to the costs just to get started.That mesh to stop animals from burrowing under the pen area is really fun to try to remove after 2 years too.Your's looks great,and should last until it doesn't ;)
Removal to replace is easy. Weed wake everything back to mesh. Grab a grinder with a diamond blade cut off peal it back. Install the new mesh role the old back over onto it.
Having to bend over to clean the run out will make you wish you hadn't.The 3rd run I built for friends was a stand-up inside height.They were tired of basically crawling through the doorway,and then raking the ground cover up.
Might find a free steel door if those popup on Marketplace in your area. Frame the end out with maybe support for the wall going back. Cover with paint or something cheap for now. Sucks post plandemic the free steel siding roofing material ain't a thing.
We had Bantam Chicken and the eggs were size of half dollar it would take about eight eggs that equal four the eggs were so super small but thank you for the video