How to define the LZ value for the Rafter shown below?

My first question is, do I need to define the value of LZ for the rafters since they will experience compression?

If so, what should be the correct value for LZ? Is it going to be 12.948m and 11.558m respectively or add 12.948 + 11.558 for the rafters?

By the way, I'm using AISC LRFD as my design code.