"I am just a young girl who isnt capable of adding a roof of some sort"
I wouldn't discount yourself simply because you're young and female. I don't know your exact age and you're not allowed to tell us.
That being said - I don't know what schools are like these days because we don't have kids, but in my school days, both the junior high and high school locations had excellent shop teachers and an on-location woodworking shop filled with all the tools necessary to make almost anything. There are many schools that have woodworking class projects (large projects) throughout the year. I remember one year we built an entire fenceline around a community member's 5 acres of land. The year following it was an actual mini-barn for another community member when theirs burnt down. Many times these projects don't cost anything to the lucky recipient but are used as a learning tool for the kids who build them. It couldn't hurt to ask if you could possibly make the "coop of your dreams" a class project and get everyone involved. It would be much more than a coop that way, and a tangible memoir for years to come for you.
Either that ..or I would possibly speak with your parents about your chickens' housing area and explain to them that it's not really up to par in regard to protection from the elements. Perhaps they'd be willing to help you get the necessary wood (many places give away shipping pallets for free actually, and you can build a lot of nice things with those). You could still ask the shop teachers in your area if you would be able to access their help and tools (mainly the neat machinery, haha) as well. If you have parental supervision, plus their supervision, there's not many things more special to a woodworker than someone taking an interest in their craft.
It could also be a worthwhile project for you to do with a couple of close friends with some free shipping pallets, a hammer and nails. Structures generally last a long time and it would be a nice building for you to talk about 10 years from now when people ask you if you did anything interesting in school.
Just a couple of suggestions that even a "young girl" is perfectly capable of doing. =)