This question may be easier than it appears. Remember, there is no "correct" answer. The principal wants to "hear you think."

If you have heard of "seasonal affective disorder" (SAD) and you anticipate many cloudy days, you might summarize the influence of dark days on the learning environment and opt for a windowless room. The important thing here is that you can come up with a logical and rational reason for your choice. If you anticipate many sunny days, you can go the other direction.

You can also speak to the importance of teaching students to "focus" on the tasks at hand. Part of this idea is that students must learn to filter out the unimportant stimuli (like what is happening outside the window) so they can be more attentive to the lesson inside the classroom. The real world is filled with a myriad of stimuli that must be filtered if one is to succeed. A favorite example involves driving a car on a highway lined with hundreds of billboards: what happens to the driver who tries to read them all? Better to teach kids to deal with it now.

And of course, conclude your answer with "But I'm certain I will do well in either room!"