Welcome to BYC!
There are so many options when it comes to coop design - the primary factors to consider are proper ventilation, security and adequate, appropriately designed space allowance for the birds being house.....from there it's a matter of picking the one that you like. Do you know how many birds you want to have? Are you planning to keep them confined to a coop/run setup at all times or will they be free ranging for part or all of each day? Do you have any breeds in mind yet - or know if you want to keep bantams, large fowl, layers or meat birds?