Here is how to change the width and length of my corrugated panels to suit your needs. This model is in inches and thus all dimensions of this tutorial are in inches.
This part only has one sketch and one extrude.
right click on the sketch and click the edit sketch button.
select the 28 inch dimension (this is the width of the sheet) and delete this dimension.
select the two points at the end of the spline by holding control while clicking each of the two points.
Give these two points a horizontal relationship.
Select the spline and you will see that this is an equation driven curve. Change the "X2" dimension (marked in red) to the dimension in inches you would like for the width of your sheet.
I chose 200 inches. Click the green check to accept the changes.
exit out of the sketch and your part will have the new width.
to change the length of the sheet, right click on the extrude feature and click the edit feature icon.
change the dimension to the desired length and accept the changes by click the green check.
Now the sheet has a length of 200 inches...
and a width of 200 inches.