after effects Expression

I need a CS4 After Effects Expression that does the following: When I type text it makes a solid background behind the text. There is a checkbox that allows me to turn off this effect. There is a color picker which allows me to select the color of the fill and another color picker for the stroke. There is a slider so I can specify opacity. There is a slider to specify padding for the top and bottom and then another slider to specify the left and right padding around the text. Background will automatically adjust when I type characters. Attached is a screenshot of what I'm talking about. As you can see the padding of the height and width are different.