Problems creating OS X installer with AppleScript
Just a hint how to start but to long to add it as comment:

Start with this:

set the_results to (display dialog "Which version of OS X Installation would you like to create?" with icon caution buttons {"OS X Mavericks", "OS X Yosemite", "OS X El Capitan"})
set button_returned to button returned of the_results
if button_returned is "OS X El Capitan" then tell application "Terminal"
    activate
    set currentTab to do script ("sudo /Applications/Install\\ OS\\ X\\ El\\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\\ OS\\ X\\ El\\ Capitan.app --nointeraction;")
end tell
if button_returned is "OS X Yosemite" then tell application "Terminal"
    activate
    ...


You still have to handle the sudo password.