my next door neighbour grows his between his fruit trees. but he has no chickens to munch on his efforts.
Chooks can dig stuff up or eat seedlings (mine did ) but how ever big you want. it depends too on if you do that co-planting thing and what your family eat too. i know very soon we'll be extending ours so we can grow more, but im not very Planned" in mine i go "yep that can go there, cus it spreads that can go there becuase its climbs that can go there because...well i think i can step over it" hopefully next year i'll grow pumkins and zukini in the chook run its self and maybe cucumbers as well (all runners and the chooks can peck between the vines)

I have a book some here 1squer meater or something and explains how much you can grow in that space and crop rotation ect.