Build a door to the outside, so you can load your trailer easily from where all your equipment and supplies are stored, and make certain your inside door swings away from the aisle.
A well-organized tack room helps you get into the habit of putting equipment and supplies in their designated spaces, even when you are in a hurry or tired at the end of a ride. Also, in an emergency, you don’t want to be rummaging through clutter to find what you need. The motto should be “a place for everything, and everything in its place.”