those coops in store are made with hobby/craft lumber and are made to look good on a shelf but, by no means will they accomodate the amount of chickens they claim, for any significant amount of time.
They are more like indoor serama cages.
Building your own is rediculously easy, and much cheaper... will last as long as you need. I know it sounds daunting, but do some homework, look at coop pictures, and frankenstein-together the different things you like into something custom made for your needs. Its a perfect learning.
Those store coops though, no way.