We had sliding doors for over 20 years and loved them even thought they didn't alway move easily. We are now redoing them in our new shop.
In our old store we had a soffit hanging down (see attached photos) that hid the tracks on top and a base on bottom that did not hide the tracks. The front and the sides of the soffit were made of plywood. The architect specified a lot of support from above and it was very really strong but I don't remember what they used. We are having a new soffit built in our new store this week and I can let you know after it is done what the contractor did.
In the photos below each panel was made out of 3/4" plywood and was 42" wide x 85" high. We changed hardware twice on it and were not happy with the ease of moving the doors. We took one off before we moved and weighed it and it came in at over 100 lbs. The tracks or hardware used (done twice) just could not support the weight.
A few years ago we did another section for Custom Corner Frames (see photo below). Different hardware and tracks were used and it worked very well. The panels were 7/8" MDF 35" wide x 90" high. We had a sign that is not shown in the photo that covered the tracks on top and there were no tracks on the bottom. The hardware use for this was the 111 tracks and the 1020 hangers from Johnson hardware seen here:
http://www.jhusa.net/111pdbp.aspx
We will be using the same tracks in our new shop but will be using the 1025 ball bearing hangers for the heavier doors. The biggest challenge we will have now is lighting behind the soffit as the sliding doors will be 4 feet deep!
Chavie