In order to build LineageOS yourself, you must first setup a build environment. Instructions to do that can be found here.
Once you setup a build environment, initialize the LineageOS repo in your working directory using this command:
repo init -u git://github.com/LineageOS/android.git -b cm-12.1
Next, initialize the device repositories, using this command:
curl --create-dirs -L -o .repo/local_manifests/local_manifest.xml -O -L https://raw.githubusercontent.com/PlatinumMaster/android_local_manifest-cprimeltemtr/cm-12.1/local_manifest.xml
Finally, to start syncing, run this command:
repo sync
Once you finished syncing, run these commands to build LineageOS:
. build/envsetup.sh && brunch cprimeltemtr