Hi! Welcome to BYC! I suggest getting a shed and converting it to a coop, or building a shed sized coop. Chicken math is real! @TwoCrows gave you some good links to coop ideas and plans. Enjoy!
TwoCrows has given you some great links to start with...build bigger than you think you'll need. The chickens will appreciate the room (they hate being crowded) and you may end up with more birds than you plan on right now.