I too am a new(ish) chicken owner and have decided that my current coop needs an expansion. I do, however, have a pretty good size run attached to it. I've enclosed it with clear tarps and my birds spend most of their time outside in the sheltered run.
In reading through various posts on this site and others, what I found is that you can temporarily get by with a smaller than ideal coop as long as the birds have access to an adequate sized run. If, like mine, all your chickens use the coop for is to roost at night and to lay in, then enlarging your little run would give your birds more usable space until you can build/buy a larger coop with a larger run.