We're adding a new one to our backyard to upgrade the size. We have a 8 x 4 x 4 run right now, but the current coop is actually inside the run and is too big to get out through the coop door. We made the run out of hardware cloth and 2x2's so it could be movable. We'll have to let the hens out to free range while we lift the run over the old coop, take it out, put the run back and then attach the new coop which will now be outside the run instead of in it, it will just be attached as most people have theirs...so, some pretty big differences for the hens.
Thanks for the responses! Scooter174, thank goodness the hens survived that and you guys were ok! It sounds like I may need to attach the new coop to the run and leave it there a few weeks before we officially take out the old one. Maybe this way they could get used to it's presence and go in and check it out if they want etc...?