Customize the "choose from List" Command in Apple Script

Hi guys,
i have the following Question.
I want to display a List in Apple Script from which i can choose an Item.
The Script works fine. However i would like to customize the dialog. For example make the text and the window size bigger. Add an icon of an app or change the Background of the Dialog field.
i would greatly appreciate if someone has any Tips.

tell application "System Events"
	set Auswahl to choose from list WindowNamen with prompt "Which Window:" default items {item 1 of WindowNamen}
end tell