If you extend your run, you could semi-enclose a bit of the run close to the coop if you wished. I agree about having more ventilation for ammonia, etc. Cleaning the coop frequently will also help.I LOVE that coop and am trying to build one almost exactly like it. 4 fullsize hens should do well in the coop and i think you're right to extend the run. If you're in for tough winters in yojr area keep in mind theyll spend more time inside than theyve been past few months and need some room not to start abusing each other.