The fabric is meant to be railroaded, which means the 118" is actually the length, not the width. There would be a seam horizontally in order to use this fabric. For your length window (128"), you'd need to buy 139" to not have seams.
OR just buy 54" - 60" wide fabric by how many yards you need, and have seams running vertically.

thank you for responding ...but i have already purchased the fabric that is 118". must it be railroaded, or can it be used vertically, off the roll -so we can just join two widths to have the vertical seams?

Is the sheer plain or does it have a design? If plain, or if you don't mind a design showing sideways, then it can be used the other way. However, there will probably be an extra charge since the fabric is harder to work with (more work) that way.

yes, the fabric is a solid. thanks for letting me know.

Cloth is strongest and hangs straightest if you hang it with the warp (warp is parallel to the selvage edges) vertically (the way you planned), with vertical seams. A tidy small seam will be almost invisible.

This is a railroaded sheer and is meant to be used so, but any sheer will hang best when sausage weights are put in the hem.
If it's very sheer, french seams should be used.

There is absolutely no reason not to do the job just as you have described it.

I've made many window treatments using the same type and width of sheer fabric. If a fabric has no pattern it is not railroaded. The sheers absolutely will hang better with the seams parallel to the selvages.

It sounds to me like your fabricator doesn't understand plain geometry, or fabric for that matter.