To get started with TWRP & MULTI-ROM, you'll need to get familiar with Git and Repo.
To initialize your local repository using the MULTI-ROM trees, use a command like this:
repo init -u git://github.com/MR-op3/manifest.git -b mr-7.1
Then to sync up:
repo sync --force-sync
Or for other devices, the old-fashioned way:
. build/envsetup.sh; lunch <device_name>
The following is from: https://github.com/Tasssadar/multirom/wiki/Porting-MultiROM
make recoveryimage # builds the recovery image
make multirom # builds multirom binary
make trampoline # builds trampoline - MultiROM's init daemon
make multirom_zip # builds multirom and trampoline and installation ZIP file
make multirom_uninstaller # builds uninstaller ZIP