If my window is 58 1/4w x 42 1/4h - is the roll 50 wide so I have to splice a piece or can I turn it the other way so I have to cut it at 58 1/4?

The maximum height of this gradient is 50", which is the width of the roll. The pattern runs continuous down the length of the roll with the opaque portion of the pattern at one end cap and fading to clear at the opposite end cap. If your window is 58 1/4 w, then you would order 5 feet (60") to cover this area. The height of the glass would be covered by the width of the roll (50").