Something like this would be cool:
PHP Code:
new GuiControl(TestControl)
{
scale = true; // something like this, to show it should be proportional to the screen size
x = .4; // equivalent to screenwidth*.4
y = .5; // equivalent to screenheight*.5
width = .5; // half the width of the screen
height = .2; // 1/4th the height of the screen
}
Edit: If it was actually proportional to the parent control, that would be best.