I build three different release flavors of Emacs:
The script I run basically just configures and builds right from the GNU source--I don't add any patches or any extraneous lisp packages. I do include the old Carbon icon on the disk image because I like it better than the new Cocoa icon but it is not enabled by default.
The builds will all build on whatever version of OS X I happen to be using at the time and so these may or may not work for you. The script now runs on a dedicated server (as opposed to my laptop) but because of the unstable nature of nighly builds, there may be days missing here and there.
Note: Recent Emacs builds (since 2009-12-09) have 64 bit Intel support in the Universal Binary. Yay!
Also Note: Recent Emacs builds (since 2012-12-16) have been built against Mac OS 10.7 (Lion) and have Lion full screen support if you are running on Lion or Mountain Lion. They also have better retina display support and are code signed. Also Yay!
From time to time people ask me if they can take a look at the build script I use. In the past I have declined because I wrote it without regard for portability and it had horrible things in it like absolute paths and hard-coded server names. Recently I moved the building to a new machine which meant fixing all of that and so I've decided to put the script up on github.
However, caveat emptor: the script started very small but over the years has become rather behemoth-y as new features have been added (building from ftp and bzr, building universal binaries, making the nice .dmg, etc.). It is not documented. That said, patches are welcome. :-)— David Caldwell