Whole Building Life Cycle LEED credit

We are working on a Core & Shell project with a developer that we work with frequently. I'm looking for advice on best approaches to achieving the Whole Building Life Cycle Assessment credit- we haven't used TALLY and done this type of analysis before. What are some approaches to achieving this credit that others have found successful? I think our options are 1/ hiring a consultant to do the assessment or 2/ learning Tally or another tool and doing the analysis ourselves. Are there other options? We do have a sustainability / LEED consultant on board.