I would never consider a reliever to be a building block. They tend to have short primes and are more useful to contending teams than building teams. However, given how weak the central division is, I don't know if I want the Tigers to be in re-building mode. They may be able to contend this year and/or next if they can get enough pitchers healthy. They might even consider not trading but extending Rodriguez so he won't opt out. It depends on how well he pitches and how well the team plays the next two months.