You really don't appreciate how hard this is to respond to. You could write many books on this topic. I certainly don't buy it that because you are a girl you'll have problems. I've worked construction. Girls are not limited in what they can do unless they want to be.
I suggest first you decide on what you want the coop to do. What is your criteria? How will you manage the chickens? Will they be locked up most of the time or free range? Will you have a run? What are your winters and summers like? Will you be hatching chickens? How pretty does your coop need to be? In suburbia especially that can be really important.
I'll give you three articles that might help. I think the ventilation and muddy run articles should be required reading for anyone building a coop. The cold weather one may or may not apply to you. Heat is usually more dangerous than cold for chickens, but if you live where it regularly gets way below zero Fahrenheit, cold might be a concern.
Pat’s Big Ol' Ventilation Page
https://www.backyardchickens.com/web/viewblog.php?id=1642-VENTILATION
Pat’s Cold Coop (winter design) page:
https://www.backyardchickens.com/web/viewblog.php?id=1642-winter-coop-temperatures
Pat’s Big Ol' Mud Page (fixing muddy runs):
https://www.backyardchickens.com/web/viewblog.php?id=1642-fix-a-muddy-run
Space is a huge issue. I've never heard of anyone complaining about having too much space. Chickens have died because of having too little space. In spite of what you read on this forum, there is no magic number for how much space you need. How much space you really need depends on your individual chickens and flock makeup, your climate, and especially on how you manage them. I find the more space I give them, the fewer behavioral problems they have and the less hard I have to work. If they have access to a lot of space whenever they are awake, they really don't need much coop space. However, if they cannot get outside when they are awake due to weather or your management techniques, the coop needs to be bigger. I encourage you to build it bigger than you think you need it and provide more roost space than you think you need so you have flexibility in case you want to hatch chicks or need to respond to a problem.
Once you decide on what you want the coop to do, you have many options. You can get a prefabricated building at Lowe’s or Home Depot. You can get a kit from a lumber yard or maybe a hardware store to build your own. Those are actually pretty easy. You can get a book on building sheds from your library or maybe Home Depot or Lowe’s. A coop is just a shed with ventilation, roosts, and nest boxes. There are designs in the coop section at the top of this page.
You can build it out wood, metal, plastic, or in many climates mostly out of wire. The number of options is just tremendous. The good part is that the chickens really don’t care. Humans are the ones that care, not the chickens.
I don’t know if this helps or not. I’ve probably made this sound more complicated than it is. What you want to do is certainly doable. Your son can get some good experiences from this. I really wish you luck.
