Well, 3m =9ft and 9x9=81, and 81devided by 4 is 20.25, so you can have twenty and a fourth a chicken! No, I'm just kidding.
If all the floorspace is available, you can probably fit 20-24 chickens in there, easily. Just remember to give them plenty of roosting space, about 8-12 inches per bird, or just under a third a meter. Some things to consider:
You might want poop boards, to save bedding under the roosts becoming soiled overnight. BYCers seem to have conflicted feelings on poop boards, but it will make them easier if they are A. Water proof and easy to wipe off, B. Easy to reach, C. Come out in lightweight, easily maneuverable pieces, and D. sprinkled with sweet PDZ or a similar deodorizer- poop drier upper.
You might want t section off a part of the shed with chicken wire, so that only you can walk around that section, and it isn't part of the chickens coop. This can be used for storage, and depending on the feeder- you can fill up their food without having to go into the actual coop. This will, of course, reduce the number of hens you can have.
You might want to install an automatic door to close the girls in at night and let them out in the morning- without you being there.
How many hens do you want? What breeds will you get?
