This page outlines the process for obtaining the Sequel Pro source code.
If you are interested in building a copy of Sequel Pro yourself, you can checkout a read-only copy of the project using Subversion.
Getting the Source Code
Using Mac OS X Terminal:
In Terminal.app enter the following commands to checkout a copy of the Sequel Pro source code on your desktop.
cd ~/Desktop svn checkout http://sequel-pro.googlecode.com/svn/trunk/ sequel-pro-read-only
Create a new repository bookmark with the location pointing to the following URL:
A list of the files in trunk will appear, right-click on the parent folder 'trunk' and choose 'Checkout…'.
Then, choose the directory where you would like to keep your checked out copy of the project, and click the Checkout button to begin the process.