So many options, so much cost.:) We built our barn to hold both the camper and some farm equipment. I went with 12' high sidewalls and wish I would have gone higher. We are locked out of 5th wheels at this point. Remember, if you want an overhead type door, you will need room for it, so a 14' high ceiling will not allow a 14' door. We used full height sliders so we wouldn't lose any more headroom. I don't mind getting out and opening the doors, but some might. We went 40' wide by 64' long. I hadn't intended to go so long, but the salesman showed me how little additional cost there was to adding 2 more 8' bays, and I'm glad I did. At 64' deep, I can leave the truck hooked up to the camper and close the doors with plenty of room to get around it for last minute packing, and it's all hooked up and ready to go in the morning. With the 40' width, I have 2 10' sliding doors, so 20' of opening to hit when I park it. It is nice to have some extra width to be able to work on the camper without running into what ever is parked next to it. You may find, as I did, that going a little bigger does not add as much cost as your first might think.