To get started with OMNI sources to build Pterodon Recovery, you'll need to get familiar with Git and Repo.
To initialize your local repository using the OMNIROM trees to build Pterodon Recovery, use a command like this:
repo init -u git://github.com/PterodonRecovery/manifest.git -b master
To initialize a shallow clone, which will save even more space, use a command like this:
repo init --depth=1 -u git://github.com/PterodonRecovery/manifest.git -b master
Then to sync up:
repo sync
Then to build for a device with recovery partition:
cd <source-dir>; export ALLOW_MISSING_DEPENDENCIES=true; . build/envsetup.sh; lunch omni_<device>-eng; mka recoveryimage
Then to build for a device without recovery partition:
cd <source-dir>; export ALLOW_MISSING_DEPENDENCIES=true; . build/envsetup.sh; lunch omni_<device>-eng; mka bootimage