We did some internal pens a while ago in an old cow palour. We have horses, goats, pigs, sheep and poultry and we wanted something that would be useful for anything should we need it. We were going to go with ready made stable panels but then decided they were expensive and restrictive. We thought about doing block work ourselves but in the end went with series of gates that made a number of different size pens.
There are dividing gates from the back wall coming forward. Then gates along the front. All dividing gates can be removed or tied back so we can have 1 large pen or five smaller pens of different sizes or any number in between.
With your dimensions I would do divisions of 6 foot but you know your building.
It was a bit of work hanging everything but I am really pleased with it.