Why do you want a dirt floor in half? Concrete is much easier to muck out.

Make your pens removeable, so that the barn can be easily reconfigured.

I didn't think it was adviseable to have cement floors under some species - for example horses as it was too hard on their legs/joints. Since I want this to be as flexible as possibe, i.e. I would be most likely to have a couple of either cows or sheep, I would like someone to be able to switch to horses.
Exactly how do you make the pens reconfigurable? is there a system you can buy on the market? And again, is there somewhere (I have googled some though not exhaustibly) where size requirements are listed?

Hi Mary,

What type of animals are you thinking if housing in your barn or maybe you're not sure yet? You can buy metal panels in different lengths that attach to each other and/or to the wall. I'm in Canada and I don't know if these suppliers are in the US too or not, but we've bought both Morand (morandindustries.com) and Hihog (you'll find it with a google search) metal panels. Abslutely indespensible for temporary set-ups. We use them in the barn and corral for our cattle and horses.
I think you're on the right track with keeping some dirt floor for the animals. Horses can get a condition called navicular that can lame them and I'm sure for long term housing it would be hard on cattle and goats, too. Short term I don't think it would be an issue.

We just built a calving barn and made the main alley way big enough for the tractor to drive through and push the manure out. Glad we did that.

Well, I think I was sleeping when I posted that message! You did say what kind of animals you were thinking of! Sorry.
So to go on with my thoughts...in our calving barn we find 12' by 12' stalls are comfortable for a cow/calf pair. We house them for 1-2 days and then they get moved out to a pen. We've had 10' by 12' and 10' by 10' stalls in the past, but its just too crowded and the calf can too easily be stepped on. We made four stalls down each side of the barn and the alley is also 12' wide so it can be temporarily divided up into more pens if needed as well as let the tractor through with a couple feet of clearance.

You could easily divide that temporarily for two sheep pens or open it back up for a cow. I've never housed horses in stalls except for a few hours so if they have to lay down I'm not sure what size is recomended.

Check out gov't Agriculture sites and possibly also an Organic Certification site may have lists of area requirments for each animal species. Hope this helps. Its fun to be able to customize your own barn.

Check out "Sloan's history of barns " and there is a boy scout handbook on farm structures , check out your county extension service for ideas . get them approved by your building inspector building department . you may be able to get one for free if you remove it in a timely fashion . from someone who wants it torn down .

Generally, you plan on a 12'x12' stall for horses. Anything less could get them cast (stuck with feet against the wall)when they lay down. I would plan on at least a 12' alley down the middle and at least 10' entrance height clearance. I really loved my sliding doors on my barn at my last house. I also had a pipe gate at the pasture end of the drive-thru barn alley so I could open up the sliders for air flow and still keep the animals out. Unloading the hay bales is a cinch when you can drive-thru.

For removable stall walls, try the livestock panels (horse grid is best) or if you want full or partially solid walls, try galvanized steel channels and slide in 2"x6" boards. Drill holes in the channels and mount on the support posts. Slide in the boards up to the height you want. I topped with hog panel to allow for air movement. If you have a way of making a groove in the top board like tongue and groove, the panel sits down inside the groove and doesn't wobble. I also made a top board with groove to secure the top of the hog panel. There is a company that makes these stall channels in painted, galvanized and aluminum. Country Manufacturing. The good part of these kind of walls is that you just slide out the boards when you need to expand the stalls.

There are many, many books on this very subject. I was looking at one about a week ago infact at Borders.

CHECK OUT : "farm arrangements " boy scout merit badge pamphlet . also Eric Sloans book "history of barns" also your county extension service & local and interlibrary loan libraries . good luck!