Ken I have built many of these and I use a simple method.
I use 4 sheets of 3/8: ply and 2" x 6" s for horizontals and verticals. Since they hang, all the forces are down rather than diagonal.
Cut your 2 verticals (2 of the 3 required) for the lefts and right sides. Cut your 2 horizontals, top and bottom, to fit in between the verts. Cut your final vertical to fit on the seam between the 2 plys and between. Square up the frame and remeasure everything.
Carefully locate the 2 plywood pieces on the frame with the seam centered on the middle vertical. Recheck for square and fasten.
Get help and flip the whole thing over and fasten the remaining 2 plywood pieces onto the frame members,again centering the seam on the middle vertical. I use deck screws. I have made them 8' x 8' square with no issues. I use straight? pressure treated 2" x 6" s for the frames. Then stain or paint. The rough sawn works for me and the 3/8" thickness keeps it light in weight. You can use thicker and saw cut it vertically for a board on board look if you want or add thin battens on top. BTW 2 doors made like this should take about 1/2 day to construct, so not a great deal of time required.
I have 3 sliders on 2 tracks, the center one bypasses and they are 8' x 8', 2 x 6 PT perimeter frame, center vertical on the 4' centerline and a diagonal brace between. They are faced on both sides with 3/8 exterior plywood rough sawn. Yes they are heavy, 4 sheets of 4 x 8 3/8 ply, but being double faced resist the tendency to warp.