Actually it was more based on that even if you don't expand, the more space they have the easier to maintain, and the healthier and less crowded the birds, so there is literally no downside. Due to many misinformed people, and flat out wrong information I often find that newcomers build too small of a coop and then are disappointed or end up with unhealthy stock and therefore have to spend more money to make their birds and themselves happier/healthier.
I'd also add the following tips:
The more airflow the better. Some of the setups I see the newcomer or typical backyarder have terrify me from that perspective. This goes hand in hand with tip #2
The drier you can make it the better. Dry coops are even more important than clean coops, moisture is what allows harmful bacteria to grow. This would also include the moisture from condensation in coops without adequate air flow.
Ignore anyone that recommends insulated or heated coops, this is Washington, it doesn't get cold enough (maybe if you're way up in the cascades) to worry about that. Birds come with wonderful natural insulation.