[webkit-help] how can i build webkit.app

[hujuncui]

Hello,
I try to build the webkit.app
I modified some code in webkit and 
run ~/Webkit/Tools/Scripts/build-webkit
and with ./run-safari command I can launch the webkit.
my question is how can I build the webkit.app? 
on website http://nightly.webkit.org/ has nightly build webkit.app 
I wan to build this kind app.
I trying to use autogen.sh in the webkit source directory. 
but remind me some packages are not installed.
so I am downloading these packages now
does my building steps are correct? 
and end of the build can I get the webkit.app?
thanks for your help

PS.
System OS: Mac OS Lion 10.7
Tools: Xcode 4.0 (gcc 4.2)