For current svn / build notes: http://dojotoolkit.org/book/dojo-book-0-9/part-4-meta-dojo-0
The first step to creating a custom build is getting the Dojo source tree. There are several places to get the source as described below.
The latest Dojo releases can be downloaded from the download section of the dojotoolkit.org project's home page. There are several prebuilt Dojo bundles available pre release. Each bundle has been tested and believed to be pretty stable. The names of the bundles should indicate what is contained in that bundle. For example, kitchen_sink contains most of what you need in Dojo except the widgets while core contains just the core features.
NOTE: the release bundles are NOT suitable to be used for a custom build. For that, you need an original source snapshot. Starting with Dojo 0.4.2, the source snapshots are in the download directory for the release, but have "-src" in their name. For instance:
http://download.dojotoolkit.org/release-0.4.2/dojo-0.4.2-src.zip
or
http://download.dojotoolkit.org/release-0.4.2/dojo-0.4.2-src.tar.gz
Dojo is built every night and bundled into a tarball hosted at archive.dojotoolkit.org. The most recent build is always available in the nightly directory. Note that this bundle has not undergone much testing and therefore may not be stable. It does however contain the latest bug fixes and feature implementations for the current release of Dojo. There is only one bundle available in the nightly directory and it contains all the code.
Dojo source code is hosted in a Subversion repository. The repository contains the latest source code and is used to create the nightly builds. There are a couple of ways to get a copy of the most up-to-date source code.
Anonymous release checkout (change 0.4.2 to the release you want): "svn co http://http://svn.dojotoolkit.org/dojo/tags/release-0.4.2"
Anonymous 0.4 branch checkout: "svn co http://svn.dojotoolkit.org/dojo/branches/0.4"
Anonymous trunk checkout: "svn co http://svn.dojotoolkit.org/dojo/trunk"