I have five hens in a 6 x 8 walk-in coop. So they have a little over 8 sq. ft. each for the days/weeks/months that they spend a LOT of time inside (as they did last winter). If you can, I would do an 8 x 8 coop. That way, if you ever go out of "chickening" you can still use it as nice storage shed. Four sq. ft. per bird is the minimum I recommend, but I can't imagine going through last winter with only 20 sq. ft for my girls. So I totally can't imagine when people recommend only 2-3 sq. ft. per bird. IMO, they might as well be stuck in a commercial poultry house at those measurements.
As for the run, the minimum I recommend is 10 sq. feet per bird. I have a very large run, and having such, I can't picture my hens making due with a 5 x 10 run.