I too prefer a run I can stand up in. The general rule of thumb is 10 ft.² per chicken of run space. You could even do an 8 x 8 run so you can come right off the coop And that would give you 64 ft.². If they are going to be in there all the time you could always make it a little bigger to give them extra room but I don’t know that they would be unhappy if you couldn’t do that.