I agree with all the above. Build bigger than you think you'll need. To give you an idea, a 4x4 coop can fit 4 birds. But let's say you start with three girls, and, two years down the road, their egg-laying rates sre starting to slow down. So you want to add some chicks. You can't raise 1 chick alone! So you get three, and now you have six girls in a coop for four.

If you're going to build your own coop, I'd build 4x6 or larger, so you can fit at least 6 chickens.
If your coop is raised, I'd recommend you make it 2 feet off the ground so you can access underneath the coop.
Vents under the eaves are perfect. To give you an idea, two rules of thumb for ventilation are 1 square foot per bird, or 1 square foot per 10 square feet of floor space. Whichever is smaller is the minimum you want. For a 4x6 coop, if you put a 2 inch vent on all sides, that would give you 3.33 square feet (20 feet x 2 inches) of year-round ventilation. That sounds good to me. Play around with numbers to find what works for you.
I would cover your windows with acrylic to let in light in the winter. Light is what stimulates egglaying, so the more light in a coop, the more productive your hens will be! In the summer, you can remove tbe acrylic to allow for more airflow.
One other suggestion: make your coop tall! Walk-in if possible. It will be much easier for you to access.
Oh, and personally, I wouldn't get only 2 chickens. Chickens are flock animals, so if one were to depart during chickhood, you'd need to rush out and find a companion for your remaining chick. Starting with 3 or 4 chicks is much easier.
Hope that helps! Let us know if you have any other questions.