Oooo, a question for a former pole barn builder!
For the bottom of the door, you can first put another "female" 'track' along its bottom edge, with the opening down. Then, make another "male" track to engage the one on the bottom of the door, shaped like a T. The top part of the T engages the female track on the bottom of the door, and then you weld brackets from the bottom end of the vertical part of the T to stand the door off the proper distance from the sidewall, and with tabs to screw it to the sidewall. Use something stiff for the brackets, like angle iron (not strap iron). You could use strap iron for the top part of the T...
For pairs of doors that meet in the middle of an opening, same idea can work. Just make a short (~6-inch) male track and mount it to the top of a post sunk exactly in the middle of the doorway. [You can probably buy this part ready-made, with tabs to mount it to the top of a 6-inch post.] That way, when the doors are closed, both vertical edges of them are confined against wind. Ideally, the post in the middle is nearly flush with the ground, so you can drive in without worrying about running over it.
When any sliding door is closed, it is essential to have working cam locks mounted on the door posts to hook into the door structure and pull it tight against the door posts.
I've seen sliding doors (lacking cam locks) flipped over and lying face down on top of the roof after a windstorm, many times.
If you haven't built the doors yet, consider making the frame from metal studs. Much lighter than wood, probably cheaper, and you can secure the door siding to them with self-tapping metal screws. However, I would use something heavier than a metal stud for the top horizontal, where the rollers mount. And, box-in the part where the rollers are mounted for even more strength. The hardest part about making doors is making them with perfectly square corners! When you're building them, it's also very important to have the frame blocked up perfectly horizontal as they lay flat on the floor. Any twist you build into them will stay after the siding is on them. That's another advantage of using steel for the frame. Wood warps, and twisted doors are no fun to work with!
-Paul