This is a pickle huh? Opinions differ, but I think the general rule for coop space is 4sqft. per bird. If you have 10 chickens you will need 40sqft. for your coop. Enclosing the whole structure will get you closer to that "magic" number. Then you would need to add an additional run which as a general rule is 10sq ft per bird or 100sq ft in your case. Now, these are general guidelines, so of course the numbers can be tweeked.
IMO. The bigger the better on both the coop and run. There may be days of bad weather or other circumstances like you said when it is not possible to free range.
Now, you may also talk to the guy who built this for you and come up with another idea. Maybe he has another customer who needs one this size and can build another larger one for you?
Good luck and let us know what solution(s) you come up with. I do like the looks of the structure, it looks nice.