Quote: "I want to make a huge one though. Like the width and height of a whole wall"
Dude, a segment is a segment so it is restricted to the same size as other segment unless you are wanting a crash.
You could however, make a single window pane the size of a whole segment.
Then make other segments for the corners, and the sides.
That way you could combine those segments when building for unlimited sized windows.
I'm pretty sure that can be done with modified copies of stock windows.
Why not just retexture a wall segment to look like a window pane if they are going to be that big?
I guess you want the glass to be breakable, huh?
If you wanted bulletproof glass, then the wall retexture method would be the quick fix. (you'd even have bullet holes/slugs in it when it gets shot)