The more space you can give them the better. I would say at least 4 to 5 square feet per bird. 12 x 12 is pretty small for 10 birds that would give you 144 square feet - if you use 5 square feet that would give you 250 square feet, turkeys poop alot so that will pile up quick and unless it's totaly covered they will churn that into mud hole after the first good rain. That's not healthy for them at all. Plus in the summer time they really need the extra space to keep cool in the south.
I spent the weekend working on a new pen. It is no where near being done and everything is a mess. You can kinda see it in the background of this picture. It will be enclose on all sides. We just put up 100 feet of horse fencing for the run to give them more room. I think they need the run to keep the fighting down and allow some room to get away if there is a fight.
You always have such good advice! I'm a little confused here, can you help? When you say five square feet, do you mean five feet, squared? (An area five feet wide and five feet long?) 'Cause wouldn't that be 25 square feet per bird? I'm hoping it is okay to temporarily house them in less space for a weekend out of town -- they aren't ready (in my opinion) to move into the big chicken coop and run yet. I have 7 birds, they'll be 8 weeks old.